Subject: Re: [PATCH v2] cxl: Export AFU error buffer via sysfs

From: Michael Neuling <[email-masked]>
Date: Wed, 20 May 2015 22:31:39 +1000

On Wed, 2015-05-20 at 22:12 +1000, Michael Neuling wrote:
> On Wed, 2015-05-20 at 16:26 +0530, Vaibhav Jain wrote:
> > Export the "AFU Error Buffer" via sysfs attribute (afu_err_buf). AFU
> > error buffer is used by the AFU to report application specific
> > errors. The contents of this buffer are AFU specific and are intended to
> > be interpreted by the application interacting with the afu.
> > 
> > Testing:
> > 	- Build against pseries le/be configs.
> > 	- Run testing with a special version of memcpy afu on a 'be'
> > 	kernel.
> > 
> > Change-log:
> > v1 -> v2
> > 	- Simplified cxl_afu_read_err_buffer to handle unaligned reads
> > 	by performing a short read.
> > 
> > Signed-off-by: Vaibhav Jain <[email-masked]>
> > ---
> >  Documentation/ABI/testing/sysfs-class-cxl | 11 ++++++
> >  drivers/misc/cxl/cxl.h                    |  7 ++++
> >  drivers/misc/cxl/pci.c                    | 60 +++++++++++++++++++++++++++++++
> >  drivers/misc/cxl/sysfs.c                  | 33 +++++++++++++++++
> >  4 files changed, 111 insertions(+)
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-class-cxl b/Documentation/ABI/testing/sysfs-class-cxl
> > index d46bba8..45e9ce3 100644
> > --- a/Documentation/ABI/testing/sysfs-class-cxl
> > +++ b/Documentation/ABI/testing/sysfs-class-cxl
> > @@ -6,6 +6,17 @@ Example: The real path of the attribute /sys/class/cxl/afu0.0s/irqs_max is
> >  
> >  Slave contexts (eg. /sys/class/cxl/afu0.0s):
> >  
> > +What:           /sys/class/cxl/<afu>/afu_err_buf
> > +Date:           September 2014
> > +Contact:        [email-masked]
> > +Description:    read only
> > +                AFU Error Buffer contents. The contents of this file are
> > +		application specific and depends on the AFU being used.
> > +		Applications interacting with the AFU can use this attribute
> > +		to know about the current error condition and take appropriate
> > +		action like logging the event etc.
> > +
> > +
> >  What:           /sys/class/cxl/<afu>/irqs_max
> >  Date:           September 2014
> >  Contact:        [email-masked]
> > diff --git a/drivers/misc/cxl/cxl.h b/drivers/misc/cxl/cxl.h
> > index a1cee47..789f077 100644
> > --- a/drivers/misc/cxl/cxl.h
> > +++ b/drivers/misc/cxl/cxl.h
> > @@ -362,6 +362,10 @@ struct cxl_afu {
> >  	struct mutex spa_mutex;
> >  	spinlock_t afu_cntl_lock;
> >  
> > +	/* AFU error buffer fields and bin attribute for sysfs */
> > +	u64 eb_len, eb_offset;
> > +	struct bin_attribute attr_eb;
> > +
> >  	/*
> >  	 * Only the first part of the SPA is used for the process element
> >  	 * linked list. The only other part that software needs to worry about
> > @@ -563,6 +567,9 @@ static inline void __iomem *_cxl_p2n_addr(struct cxl_afu *afu, cxl_p2n_reg_t reg
> >  u16 cxl_afu_cr_read16(struct cxl_afu *afu, int cr, u64 off);
> >  u8 cxl_afu_cr_read8(struct cxl_afu *afu, int cr, u64 off);
> >  
> > +ssize_t cxl_afu_read_err_buffer(struct cxl_afu *afu, char *buf,
> > +				loff_t off, size_t count);
> > +
> >  
> >  struct cxl_calls {
> >  	void (*cxl_slbia)(struct mm_struct *mm);
> > diff --git a/drivers/misc/cxl/pci.c b/drivers/misc/cxl/pci.c
> > index 1ef0164..162a8fc 100644
> > --- a/drivers/misc/cxl/pci.c
> > +++ b/drivers/misc/cxl/pci.c
> > @@ -593,6 +593,22 @@ static int cxl_read_afu_descriptor(struct cxl_afu *afu)
> >  	afu->crs_len = AFUD_CR_LEN(val) * 256;
> >  	afu->crs_offset = AFUD_READ_CR_OFF(afu);
> >  
> > +
> > +	/* eb_len is in multiple of 4K */
> > +	afu->eb_len = AFUD_EB_LEN(AFUD_READ_EB(afu)) * 4096;
> > +	afu->eb_offset = AFUD_READ_EB_OFF(afu);
> > +
> > +	/* eb_off is 4K aligned so lower 12 bits are always zero */
> > +	if (EXTRACT_PPC_BITS(afu->eb_offset, 0, 11) != 0) {
> > +		dev_warn(&afu->dev,
> > +			 "Invalid AFU error buffer offset %Lx\n",
> > +			 afu->eb_offset);
> > +		dev_info(&afu->dev,
> > +			 "Ignoring AFU error buffer in the descriptor\n");
> > +		/* indicate that no afu buffer exists */
> > +		afu->eb_len = 0;
> > +	}
> > +
> >  	return 0;
> >  }
> >  
> > @@ -672,6 +688,50 @@ static int sanitise_afu_regs(struct cxl_afu *afu)
> >  	return 0;
> >  }
> >  
> > +/*
> > + * afu_eb_read:
> > + * Called from sysfs and reads the afu error info buffer. The h/w only supports
> > + * 4/8 bytes aligned access. So most of the code tries to get around this by
> > + * reading full 8 bytes aligned chunks, copying it to a temp buffer and dropping
> > + * unneeded bytes at the beginning & the end of the requested region.
> > + */
> > +ssize_t cxl_afu_read_err_buffer(struct cxl_afu *afu, char *buf,
> > +				loff_t off, size_t count)
> > +{
> > +	u8 tbuff[8];
> > +	const void __iomem *ebuf = afu->afu_desc_mmio + afu->eb_offset;
> > +
> > +	count = min((size_t)(afu->eb_len - off), count);
> > +
> > +	if (unlikely(count <= 0)) {
> > +		/* handle case where no ebuf exists or offset out of bound */
> > +		count = 0;
> > +
> > +	} else if ((count >= 8) && IS_ALIGNED(off, 8)) {
> > +		/* read all the intermediate aligned words */
> > +
> > +		count = round_down(off + count, 8) - off;
> > +		_memcpy_fromio(buf,
> > +			       ebuf + off, count);
> > +
> > +	} else if (!IS_ALIGNED(off, 8)) {
> > +		/* handle unaligned access at the beginning */
> > +		_memcpy_fromio(tbuff, ebuf + round_down(off, 8), 8);
> > +
> > +		count = min((size_t)(ALIGN(off, 8) - off), count);
> > +		memcpy(buf, tbuff + (off & 0x7), count);
> > +
> > +	} else {
> > +		/* offset is aligned but count < 8 */
> > +		_memcpy_fromio(tbuff, ebuf + round_down(off + count, 8), 8);
> > +
> > +		count = (off + count) - round_down(off + count, 8);
> > +		memcpy(buf, tbuff, count);
> > +	}
> 
> I still think this is too complex.  How about something like this where
> we always use a copy buffer (completely untested):
> 
>         copy_size_max = PAGESIZE;
>         
>         ebuf_start = round_down(off, 8);
>         ebuf_length = min(count + 16, copy_size_max); // copy extra for alignment at start and end
>         count = min(count, copy_size_max);  // Adjust for max copy
>         length
>         count = count - (off & 7); // Adjust for non aligned offset
>         
>         tbuff = __get_free_page(GFP_KERNEL);
>         
>         _memcpy_fromio(tbuff, ebuf_start, ebuf_length);
>         memcpy(buf, tbuff + (off & 0x7), count); // grab what we need
>         
>         free_page(tbuff);
>         
>         return count;

Slightly updated version as there was a bug in the count calculation.
Still untested.

                copy_size_max = PAGESIZE;
                
                ebuf_start = round_down(off, 8);
                ebuf_length = min(count + 16, copy_size_max); // copy extra for alignment at start and end
                if ((count + (off & 7)) > copy_size_max)
                   /* adjust count if we go past copy_size_max */
                   count = copy_size_max - (off & 7);
                
                tbuff = __get_free_page(GFP_KERNEL);
                
                _memcpy_fromio(tbuff, ebuf_start, ebuf_length);
                memcpy(buf, tbuff + (off & 0x7), count); // grab what we need
                
                free_page(tbuff);
                
                return count;

Mikey

>         
> Mikey
> 
> 
> > +
> > +	return count;
> > +}
> > +
> >  static int cxl_init_afu(struct cxl *adapter, int slice, struct pci_dev *dev)
> >  {
> >  	struct cxl_afu *afu;
> > diff --git a/drivers/misc/cxl/sysfs.c b/drivers/misc/cxl/sysfs.c
> > index d0c38c7..4942d55 100644
> > --- a/drivers/misc/cxl/sysfs.c
> > +++ b/drivers/misc/cxl/sysfs.c
> > @@ -356,6 +356,16 @@ static ssize_t api_version_compatible_show(struct device *device,
> >  	return scnprintf(buf, PAGE_SIZE, "%i\n", CXL_API_VERSION_COMPATIBLE);
> >  }
> >  
> > +static ssize_t afu_eb_read(struct file *filp, struct kobject *kobj,
> > +			       struct bin_attribute *bin_attr, char *buf,
> > +			       loff_t off, size_t count)
> > +{
> > +	struct cxl_afu *afu = to_cxl_afu(container_of(kobj,
> > +						      struct device, kobj));
> > +
> > +	return cxl_afu_read_err_buffer(afu, buf, off, count);
> > +}
> > +
> >  static struct device_attribute afu_attrs[] = {
> >  	__ATTR_RO(mmio_size),
> >  	__ATTR_RO(irqs_min),
> > @@ -534,6 +544,10 @@ void cxl_sysfs_afu_remove(struct cxl_afu *afu)
> >  	struct afu_config_record *cr, *tmp;
> >  	int i;
> >  
> > +	/* remove the err buffer bin attribute */
> > +	if (afu->eb_len)
> > +		device_remove_bin_file(&afu->dev, &afu->attr_eb);
> > +
> >  	for (i = 0; i < ARRAY_SIZE(afu_attrs); i++)
> >  		device_remove_file(&afu->dev, &afu_attrs[i]);
> >  
> > @@ -555,6 +569,22 @@ int cxl_sysfs_afu_add(struct cxl_afu *afu)
> >  			goto err;
> >  	}
> >  
> > +	/* conditionally create the add the binary file for error info buffer */
> > +	if (afu->eb_len) {
> > +		afu->attr_eb.attr.name = "afu_err_buff";
> > +		afu->attr_eb.attr.mode = S_IRUGO;
> > +		afu->attr_eb.size = afu->eb_len;
> > +		afu->attr_eb.read = afu_eb_read;
> > +
> > +		rc = device_create_bin_file(&afu->dev, &afu->attr_eb);
> > +		if (rc) {
> > +			dev_err(&afu->dev,
> > +				"Unable to create eb attr for the afu. Err(%d)\n",
> > +				rc);
> > +			goto err;
> > +		}
> > +	}
> > +
> >  	for (i = 0; i < afu->crs_num; i++) {
> >  		cr = cxl_sysfs_afu_new_cr(afu, i);
> >  		if (IS_ERR(cr)) {
> > @@ -570,6 +600,9 @@ err1:
> >  	cxl_sysfs_afu_remove(afu);
> >  	return rc;
> >  err:
> > +	/* reset the eb_len as we havent created the bin attr */
> > +	afu->eb_len = 0;
> > +
> >  	for (i--; i >= 0; i--)
> >  		device_remove_file(&afu->dev, &afu_attrs[i]);
> >  	return rc;
>