Subject: Re: [PATCH 10/65] powerpc/mm: Drop WIMG in favour of new constants

From: Balbir Singh <[email-masked]>
Date: Tue, 5 Apr 2016 23:25:28 +1000

On 27/03/16 19:23, Aneesh Kumar K.V wrote:
> PowerISA 3.0 introduce two pte bits with the below meaning w.r.t Radix
> 00 ->  Normal Memory
> 01 ->  Strong Access Order
> 10 -> Non idempotent I/O (Cache inhibited and guarded)
> 11 -> Tolerant I/O (Cache inhibited)
>
> We drop the existing WIMG bits in linux page table in favour of above
> constants. We loose _PAGE_WRITETHRU with this conversion. We only use
> writethru via pgprot_cached_wthru() which is used by fbdev/controlfb.c
> which is Apple control display and also PPC32.
>
> With respect to _PAGE_COHERENCE, we have been marking hpte
> always coherent for some time now. htab_convert_pte_flags always added
> HPTE_R_M.
>
> NOTE: KVM changes need closer review.
>
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
> ---
>  arch/powerpc/include/asm/book3s/64/hash.h | 72 ++++++++++++++-----------------
>  arch/powerpc/include/asm/kvm_book3s_64.h  | 27 +++++-------
>  arch/powerpc/kvm/book3s_64_mmu_hv.c       | 11 +++--
>  arch/powerpc/kvm/book3s_hv_rm_mmu.c       | 12 +++---
>  arch/powerpc/mm/hash64_64k.c              |  2 +-
>  arch/powerpc/mm/hash_utils_64.c           | 18 ++++----
>  arch/powerpc/mm/pgtable.c                 |  8 ++--
>  arch/powerpc/mm/pgtable_64.c              |  4 --
>  arch/powerpc/platforms/pseries/lpar.c     |  4 --
>  9 files changed, 67 insertions(+), 91 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h
> index 2a80981f1b0b..fd2d0ebfc49c 100644
> --- a/arch/powerpc/include/asm/book3s/64/hash.h
> +++ b/arch/powerpc/include/asm/book3s/64/hash.h
> @@ -20,12 +20,10 @@
>  #define _PAGE_READ		0x00004	/* read access allowed */
>  #define _PAGE_RW		(_PAGE_READ | _PAGE_WRITE)
>  #define _PAGE_RWX		(_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC)
> -#define _PAGE_PRIVILEGED	0x00008 /* kernel access only */ 
This change is redundant
> -#define _PAGE_GUARDED		0x00010 /* G: guarded (side-effect) page */
> -/* M (memory coherence) is always set in the HPTE, so we don't need it here */
> -#define _PAGE_COHERENT		0x0
> -#define _PAGE_NO_CACHE		0x00020 /* I: cache inhibit */
> -#define _PAGE_WRITETHRU		0x00040 /* W: cache write-through */
> +#define _PAGE_PRIVILEGED	0x00008 /* kernel access only */
We add it right back here
> +#define _PAGE_SAO		0x00010 /* Strong access order */
> +#define _PAGE_NON_IDEMPOTENT	0x00020 /* non idempotent memory */
I think the comment is not very useful, it just calls out the defines
> +#define _PAGE_TOLERANT		0x00030 /* tolerant memory, cache inhibited */
>  #define _PAGE_DIRTY		0x00080 /* C: page changed */
>  #define _PAGE_ACCESSED		0x00100 /* R: page referenced */
>  #define _PAGE_SPECIAL		0x00400 /* software: special page */
> @@ -43,7 +41,12 @@
>  #define _PAGE_HASHPTE		(1ul << 61)	/* PTE has associated HPTE */
>  #define _PAGE_PTE		(1ul << 62)	/* distinguishes PTEs from pointers */
>  #define _PAGE_PRESENT		(1ul << 63)	/* pte contains a translation */
> -
> +/*
> + * Drivers request for cache inhibited pte mapping using _PAGE_NO_CACHE
> + * Instead of fixing all of them, add an alternate define which
> + * maps CI pte mapping.
> + */
> +#define _PAGE_NO_CACHE		_PAGE_TOLERANT
>  /*
>   * We need to differentiate between explicit huge page and THP huge
>   * page, since THP huge page also need to track real subpage details
> @@ -122,9 +125,6 @@
>  #define _PAGE_KERNEL_RWX	(_PAGE_PRIVILEGED | _PAGE_DIRTY | \
>  				 _PAGE_RW | _PAGE_EXEC)
>  
> -/* Strong Access Ordering */
> -#define _PAGE_SAO		(_PAGE_WRITETHRU | _PAGE_NO_CACHE | _PAGE_COHERENT)
> -
>  /* No page size encoding in the linux PTE */
>  #define _PAGE_PSIZE		0
>  
> @@ -150,10 +150,9 @@
>  /*
>   * Mask of bits returned by pte_pgprot()
>   */
> -#define PAGE_PROT_BITS	(_PAGE_GUARDED | _PAGE_COHERENT | _PAGE_NO_CACHE | \
> -			 _PAGE_WRITETHRU | _PAGE_4K_PFN | \
> -			 _PAGE_PRIVILEGED | _PAGE_ACCESSED |  _PAGE_READ |\
> -			 _PAGE_WRITE |  _PAGE_DIRTY | _PAGE_EXEC | \
> +#define PAGE_PROT_BITS  (_PAGE_SAO | _PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT | \
> +			 _PAGE_4K_PFN | _PAGE_PRIVILEGED | _PAGE_ACCESSED | \
> +			 _PAGE_READ | _PAGE_WRITE |  _PAGE_DIRTY | _PAGE_EXEC | \
>  			 _PAGE_SOFT_DIRTY)
>  /*
>   * We define 2 sets of base prot bits, one for basic pages (ie,
> @@ -162,7 +161,7 @@
>   * the processor might need it for DMA coherency.
>   */
>  #define _PAGE_BASE_NC	(_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_PSIZE)
> -#define _PAGE_BASE	(_PAGE_BASE_NC | _PAGE_COHERENT)
> +#define _PAGE_BASE	(_PAGE_BASE_NC)
>  
>  /* Permission masks used to generate the __P and __S table,
>   *
> @@ -203,9 +202,9 @@
>  /* Permission masks used for kernel mappings */
>  #define PAGE_KERNEL	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RW)
>  #define PAGE_KERNEL_NC	__pgprot(_PAGE_BASE_NC | _PAGE_KERNEL_RW | \
> -				 _PAGE_NO_CACHE)
> +				 _PAGE_TOLERANT)
I don't think this change is required given that _PAGE_NO_CACHE is _PAGE_TOLERANT
>  #define PAGE_KERNEL_NCG	__pgprot(_PAGE_BASE_NC | _PAGE_KERNEL_RW | \
> -				 _PAGE_NO_CACHE | _PAGE_GUARDED)
> +				 _PAGE_NON_IDEMPOTENT)
>  #define PAGE_KERNEL_X	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RWX)
>  #define PAGE_KERNEL_RO	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RO)
>  #define PAGE_KERNEL_ROX	__pgprot(_PAGE_BASE | _PAGE_KERNEL_ROX)
> @@ -512,45 +511,26 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
>  	*ptep = pte;
>  }
>  
> -/*
> - * Macro to mark a page protection value as "uncacheable".
> - */
> -
> -#define _PAGE_CACHE_CTL	(_PAGE_COHERENT | _PAGE_GUARDED | _PAGE_NO_CACHE | \
> -			 _PAGE_WRITETHRU)
> +#define _PAGE_CACHE_CTL	(_PAGE_NON_IDEMPOTENT | _PAGE_TOLERANT)
>  
>  #define pgprot_noncached pgprot_noncached
>  static inline pgprot_t pgprot_noncached(pgprot_t prot)
>  {
>  	return __pgprot((pgprot_val(prot) & ~_PAGE_CACHE_CTL) |
> -			_PAGE_NO_CACHE | _PAGE_GUARDED);
> +			_PAGE_NON_IDEMPOTENT);
>  }
>  
>  #define pgprot_noncached_wc pgprot_noncached_wc
>  static inline pgprot_t pgprot_noncached_wc(pgprot_t prot)
>  {
>  	return __pgprot((pgprot_val(prot) & ~_PAGE_CACHE_CTL) |
> -			_PAGE_NO_CACHE);
> +			_PAGE_TOLERANT);
Same as before
>  }
>  
>  #define pgprot_cached pgprot_cached
>  static inline pgprot_t pgprot_cached(pgprot_t prot)
>  {
> -	return __pgprot((pgprot_val(prot) & ~_PAGE_CACHE_CTL) |
> -			_PAGE_COHERENT);
> -}
> -
> -#define pgprot_cached_wthru pgprot_cached_wthru
> -static inline pgprot_t pgprot_cached_wthru(pgprot_t prot)
> -{
> -	return __pgprot((pgprot_val(prot) & ~_PAGE_CACHE_CTL) |
> -			_PAGE_COHERENT | _PAGE_WRITETHRU);
> -}
> -
> -#define pgprot_cached_noncoherent pgprot_cached_noncoherent
> -static inline pgprot_t pgprot_cached_noncoherent(pgprot_t prot)
> -{
> -	return __pgprot(pgprot_val(prot) & ~_PAGE_CACHE_CTL);
> +	return __pgprot((pgprot_val(prot) & ~_PAGE_CACHE_CTL));
>  }
>  
>  #define pgprot_writecombine pgprot_writecombine
> @@ -558,6 +538,18 @@ static inline pgprot_t pgprot_writecombine(pgprot_t prot)
>  {
>  	return pgprot_noncached_wc(prot);
>  }
> +/*
> + * check a pte mapping have cache inhibited property
> + */
> +static inline bool pte_ci(pte_t pte)
> +{
> +	unsigned long pte_v = pte_val(pte);
> +
> +	if (((pte_v & _PAGE_CACHE_CTL) == _PAGE_TOLERANT) ||
> +	    ((pte_v & _PAGE_CACHE_CTL) == _PAGE_NON_IDEMPOTENT))
> +		return true;
> +	return false;
> +}
>  
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  extern void hpte_do_hugepage_flush(struct mm_struct *mm, unsigned long addr,
> diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
> index f9a7a89a3e4f..ebdaf576cf26 100644
> --- a/arch/powerpc/include/asm/kvm_book3s_64.h
> +++ b/arch/powerpc/include/asm/kvm_book3s_64.h
> @@ -278,19 +278,24 @@ static inline unsigned long hpte_make_readonly(unsigned long ptel)
>  	return ptel;
>  }
>  
> -static inline int hpte_cache_flags_ok(unsigned long ptel, unsigned long io_type)
> +static inline bool hpte_cache_flags_ok(unsigned long hptel, bool is_ci)
>  {
> -	unsigned int wimg = ptel & HPTE_R_WIMG;
> +	unsigned int wimg = hptel & HPTE_R_WIMG;
>  
>  	/* Handle SAO */
>  	if (wimg == (HPTE_R_W | HPTE_R_I | HPTE_R_M) &&
>  	    cpu_has_feature(CPU_FTR_ARCH_206))
>  		wimg = HPTE_R_M;
>  
> -	if (!io_type)
> +	if (!is_ci)
>  		return wimg == HPTE_R_M;
> -
> -	return (wimg & (HPTE_R_W | HPTE_R_I)) == io_type;
> +	/*
> +	 * if host is mapped cache inhibited, make sure hptel also have
> +	 * cache inhibited.
> +	 */
The comment applies to the !!(wimg & HPTE_R_I)
> +	if (wimg & HPTE_R_W) /* FIXME!! is this ok for all guest. ? */
> +		return false;
This says the page cannot be cache inhibited and writethrough?
> +	return !!(wimg & HPTE_R_I);
>  }
>  
>  /*
> @@ -333,18 +338,6 @@ static inline pte_t kvmppc_read_update_linux_pte(pte_t *ptep, int writing)
>  	return new_pte;
>  }
>  
> -
> -/* Return HPTE cache control bits corresponding to Linux pte bits */
> -static inline unsigned long hpte_cache_bits(unsigned long pte_val)
> -{
> -#if _PAGE_NO_CACHE == HPTE_R_I && _PAGE_WRITETHRU == HPTE_R_W
> -	return pte_val & (HPTE_R_W | HPTE_R_I);
> -#else
> -	return ((pte_val & _PAGE_NO_CACHE) ? HPTE_R_I : 0) +
> -		((pte_val & _PAGE_WRITETHRU) ? HPTE_R_W : 0);
> -#endif
> -}
> -
>  static inline bool hpte_read_permission(unsigned long pp, unsigned long key)
>  {
>  	if (key)
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index c7b78d8336b2..05f09ae82587 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -447,7 +447,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
>  	struct revmap_entry *rev;
>  	struct page *page, *pages[1];
>  	long index, ret, npages;
> -	unsigned long is_io;
> +	bool is_ci;
>  	unsigned int writing, write_ok;
>  	struct vm_area_struct *vma;
>  	unsigned long rcbits;
> @@ -503,7 +503,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
>  	smp_rmb();
>  
>  	ret = -EFAULT;
> -	is_io = 0;
> +	is_ci = false;
>  	pfn = 0;
>  	page = NULL;
>  	pte_size = PAGE_SIZE;
> @@ -521,7 +521,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
>  			pfn = vma->vm_pgoff +
>  				((hva - vma->vm_start) >> PAGE_SHIFT);
>  			pte_size = psize;
> -			is_io = hpte_cache_bits(pgprot_val(vma->vm_page_prot));
> +			is_ci = pte_ci(__pte((pgprot_val(vma->vm_page_prot))));
>  			write_ok = vma->vm_flags & VM_WRITE;
>  		}
>  		up_read(&current->mm->mmap_sem);
> @@ -558,10 +558,9 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
>  		goto out_put;
>  
>  	/* Check WIMG vs. the actual page we're accessing */
> -	if (!hpte_cache_flags_ok(r, is_io)) {
> -		if (is_io)
> +	if (!hpte_cache_flags_ok(r, is_ci)) {
> +		if (is_ci)
>  			goto out_put;
> -
>  		/*
>  		 * Allow guest to map emulated device memory as
>  		 * uncacheable, but actually make it cacheable.
> diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> index 4cb8db05f3e5..99b4e9d5dd23 100644
> --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> @@ -175,7 +175,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
>  	unsigned long g_ptel;
>  	struct kvm_memory_slot *memslot;
>  	unsigned hpage_shift;
> -	unsigned long is_io;
> +	bool is_ci;
>  	unsigned long *rmap;
>  	pte_t *ptep;
>  	unsigned int writing;
> @@ -199,7 +199,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
>  	gfn = gpa >> PAGE_SHIFT;
>  	memslot = __gfn_to_memslot(kvm_memslots_raw(kvm), gfn);
>  	pa = 0;
> -	is_io = ~0ul;
> +	is_ci = false;
>  	rmap = NULL;
>  	if (!(memslot && !(memslot->flags & KVM_MEMSLOT_INVALID))) {
>  		/* Emulated MMIO - mark this with key=31 */
> @@ -250,7 +250,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
>  			if (writing && !pte_write(pte))
>  				/* make the actual HPTE be read-only */
>  				ptel = hpte_make_readonly(ptel);
> -			is_io = hpte_cache_bits(pte_val(pte));
> +			is_ci = pte_ci(pte);
>  			pa = pte_pfn(pte) << PAGE_SHIFT;
>  			pa |= hva & (host_pte_size - 1);
>  			pa |= gpa & ~PAGE_MASK;
> @@ -267,9 +267,9 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
>  	else
>  		pteh |= HPTE_V_ABSENT;
>  
> -	/* Check WIMG */
> -	if (is_io != ~0ul && !hpte_cache_flags_ok(ptel, is_io)) {
> -		if (is_io)
> +	/*If we had host pte mapping then  Check WIMG */
> +	if (ptep && !hpte_cache_flags_ok(ptel, is_ci)) {
> +		if (is_ci)
>  			return H_PARAMETER;
>  		/*
>  		 * Allow guest to map emulated device memory as
> diff --git a/arch/powerpc/mm/hash64_64k.c b/arch/powerpc/mm/hash64_64k.c
> index f33b410d6c8a..419562b0e9c8 100644
> --- a/arch/powerpc/mm/hash64_64k.c
> +++ b/arch/powerpc/mm/hash64_64k.c
> @@ -248,7 +248,7 @@ int __hash_page_64K(unsigned long ea, unsigned long access,
>  		 * If so, bail out and refault as a 4k page
>  		 */
>  		if (!mmu_has_feature(MMU_FTR_CI_LARGE_PAGE) &&
> -		    unlikely(old_pte & _PAGE_NO_CACHE))
> +		    unlikely(pte_ci(pte)))
>  			return 0;
>  		/*
>  		 * Try to lock the PTE, add ACCESSED and DIRTY if it was
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index 59d4600bacd5..e924690a5a0e 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -192,12 +192,13 @@ unsigned long htab_convert_pte_flags(unsigned long pteflags)
>  	/*
>  	 * Add in WIG bits
>  	 */
> -	if (pteflags & _PAGE_WRITETHRU)
> -		rflags |= HPTE_R_W;
> -	if (pteflags & _PAGE_NO_CACHE)
> +
> +	if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_TOLERANT)
>  		rflags |= HPTE_R_I;
> -	if (pteflags & _PAGE_GUARDED)
> -		rflags |= HPTE_R_G;
> +	if ((pteflags & _PAGE_CACHE_CTL ) == _PAGE_NON_IDEMPOTENT)
> +		rflags |= (HPTE_R_I | HPTE_R_G);
> +	if ((pteflags & _PAGE_CACHE_CTL) == _PAGE_SAO)
> +		rflags |= (HPTE_R_I | HPTE_R_W);
>  
>  	return rflags;
>  }
> @@ -1138,8 +1139,7 @@ int hash_page_mm(struct mm_struct *mm, unsigned long ea,
>  	/* If this PTE is non-cacheable and we have restrictions on
>  	 * using non cacheable large pages, then we switch to 4k
>  	 */
> -	if (mmu_ci_restrictions && psize == MMU_PAGE_64K &&
> -	    (pte_val(*ptep) & _PAGE_NO_CACHE)) {
> +	if (mmu_ci_restrictions && psize == MMU_PAGE_64K && pte_ci(*ptep)) {
>  		if (user_region) {
>  			demote_segment_4k(mm, ea);
>  			psize = MMU_PAGE_4K;
> @@ -1293,13 +1293,13 @@ void hash_preload(struct mm_struct *mm, unsigned long ea,
>  
>  	WARN_ON(hugepage_shift);
>  #ifdef CONFIG_PPC_64K_PAGES
> -	/* If either _PAGE_4K_PFN or _PAGE_NO_CACHE is set (and we are on
> +	/* If either _PAGE_4K_PFN or cache inhibited is set (and we are on
>  	 * a 64K kernel), then we don't preload, hash_page() will take
>  	 * care of it once we actually try to access the page.
>  	 * That way we don't have to duplicate all of the logic for segment
>  	 * page size demotion here
>  	 */
> -	if (pte_val(*ptep) & (_PAGE_4K_PFN | _PAGE_NO_CACHE))
> +	if ((pte_val(*ptep) & _PAGE_4K_PFN) || pte_ci(*ptep))
>  		goto out_exit;
>  #endif /* CONFIG_PPC_64K_PAGES */
>  
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index a34884beaa47..115a0a19d5a2 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -38,16 +38,16 @@ static inline int is_exec_fault(void)
>  
>  /* We only try to do i/d cache coherency on stuff that looks like
>   * reasonably "normal" PTEs. We currently require a PTE to be present
> - * and we avoid _PAGE_SPECIAL and _PAGE_NO_CACHE. We also only do that
> + * and we avoid _PAGE_SPECIAL and cache inhibited pte. We also only do that
>   * on userspace PTEs
>   */
>  static inline int pte_looks_normal(pte_t pte)
>  {
>  
>  #if defined(CONFIG_PPC_BOOK3S_64)
> -	if ((pte_val(pte) &
> -	     (_PAGE_PRESENT | _PAGE_SPECIAL | _PAGE_NO_CACHE)) ==
> -	    _PAGE_PRESENT) {
> +	if ((pte_val(pte) & (_PAGE_PRESENT | _PAGE_SPECIAL)) == _PAGE_PRESENT) {
> +		if (pte_ci(pte))
> +			return 0;
>  		if (pte_user(pte))
>  			return 1;
>  	}
> diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
> index 6f1b7064f822..db924c54f370 100644
> --- a/arch/powerpc/mm/pgtable_64.c
> +++ b/arch/powerpc/mm/pgtable_64.c
> @@ -167,10 +167,6 @@ void __iomem * __ioremap_at(phys_addr_t pa, void *ea, unsigned long size,
>  	if ((flags & _PAGE_PRESENT) == 0)
>  		flags |= pgprot_val(PAGE_KERNEL);
>  
> -	/* Non-cacheable page cannot be coherent */
> -	if (flags & _PAGE_NO_CACHE)
> -		flags &= ~_PAGE_COHERENT;
> -
>  	/* We don't support the 4K PFN hack with ioremap */
>  	if (flags & _PAGE_4K_PFN)
>  		return NULL;
> diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
> index 2415a0d31f8f..0d4608990702 100644
> --- a/arch/powerpc/platforms/pseries/lpar.c
> +++ b/arch/powerpc/platforms/pseries/lpar.c
> @@ -152,10 +152,6 @@ static long pSeries_lpar_hpte_insert(unsigned long hpte_group,
>  	/* Exact = 0                   */
>  	flags = 0;
>  
> -	/* Make pHyp happy */
> -	if ((rflags & _PAGE_NO_CACHE) && !(rflags & _PAGE_WRITETHRU))
> -		hpte_r &= ~HPTE_R_M;
> -
>  	if (firmware_has_feature(FW_FEATURE_XCMO) && !(hpte_r & HPTE_R_N))
>  		flags |= H_COALESCE_CAND;
>  

Balbir