Subject: Re: [PATCH v3 18/26] PCI: endpoint: Add support to allocate aligned buffers to be mapped in BARs

From: Lorenzo Pieralisi <[email-masked]>
Date: Fri, 12 Apr 2019 11:55:20 +0100

On Fri, Apr 12, 2019 at 04:07:49PM +0530, Kishon Vijay Abraham I wrote:
> Hi Lorenzo,
> 
> On 11/04/19 9:02 PM, Lorenzo Pieralisi wrote:
> > On Mon, Mar 25, 2019 at 03:09:39PM +0530, Kishon Vijay Abraham I wrote:
> >> Modify pci_epf_alloc_space API to take alignment size as argument in
> >> order to argument in order to allocate aligned buffers to be mapped to
> >> BARs.
> >>
> >> Add 'align' parameter to epc_features which can be used by platform
> >> drivers to specifiy the BAR allocation alignment requirements and use
> >> this while invoking pci_epf_alloc_space.
> >>
> >> This is mainly required for Synopsys Designware PCIe core which masks
> >> the lower bits based on the BAR size (See "I/O and MEM Match Modes"
> >> section in DesignWare Cores PCI Express Controller Databook version
> >> 4.90a).
> > 
> > Hi Kishon,
> > 
> > isn't this a generic PCI BAR requirement rather than a Designware
> > specific one ?
> > 
> > The patch is fine I just would like to understand the statement above.
> 
> The address that is allocated using pci_epf_alloc_space would be directly
> written to the target address of the Inbound address translation unit.
> Designware IP has a configuration parameter (CX_ATU_MIN_REGION_SIZE [1]) which
> has 64KB as default value and the lower 16 bits of the Base, Limit and Target
> registers of the Inbound ATU are fixed to zero.  So if the programmed memory
> address is not aligned to 64 KB boundary there will be memory corruption.
> 
> PCI spec has restrictions on the minimum memory address range requested by BAR
> as 128 Bytes and the size to be a power of 2, however it doesn't have any
> restriction on the local endpoint memory addresses that are mapped to BAR. That
> is an endpoint controller restriction.
> 
> [1] -> http://www.ti.com/lit/ug/spruid7c/spruid7c.pdf

That's much clearer, it should go into the commit log, I will try
to update it myself and notify you when I push it out.

Lorenzo

> Thanks
> Kishon
> 
> > Thanks,
> > Lorenzo
> > 
> >> Signed-off-by: Kishon Vijay Abraham I <[email-masked]>
> >> ---
> >>  drivers/pci/endpoint/functions/pci-epf-test.c |  5 +++--
> >>  drivers/pci/endpoint/pci-epf-core.c           | 10 ++++++++--
> >>  include/linux/pci-epc.h                       |  2 ++
> >>  include/linux/pci-epf.h                       |  3 ++-
> >>  4 files changed, 15 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> >> index d0b91da49bf4..c0786ca74312 100644
> >> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> >> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> >> @@ -438,7 +438,7 @@ static int pci_epf_test_alloc_space(struct pci_epf *epf)
> >>  	epc_features = epf_test->epc_features;
> >>  
> >>  	base = pci_epf_alloc_space(epf, sizeof(struct pci_epf_test_reg),
> >> -				   test_reg_bar);
> >> +				   test_reg_bar, epc_features->align);
> >>  	if (!base) {
> >>  		dev_err(dev, "Failed to allocated register space\n");
> >>  		return -ENOMEM;
> >> @@ -453,7 +453,8 @@ static int pci_epf_test_alloc_space(struct pci_epf *epf)
> >>  		if (!!(epc_features->reserved_bar & (1 << bar)))
> >>  			continue;
> >>  
> >> -		base = pci_epf_alloc_space(epf, bar_size[bar], bar);
> >> +		base = pci_epf_alloc_space(epf, bar_size[bar], bar,
> >> +					   epc_features->align);
> >>  		if (!base)
> >>  			dev_err(dev, "Failed to allocate space for BAR%d\n",
> >>  				bar);
> >> diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c
> >> index 8bfdcd291196..fb1306de8f40 100644
> >> --- a/drivers/pci/endpoint/pci-epf-core.c
> >> +++ b/drivers/pci/endpoint/pci-epf-core.c
> >> @@ -109,10 +109,12 @@ EXPORT_SYMBOL_GPL(pci_epf_free_space);
> >>   * pci_epf_alloc_space() - allocate memory for the PCI EPF register space
> >>   * @size: the size of the memory that has to be allocated
> >>   * @bar: the BAR number corresponding to the allocated register space
> >> + * @align: alignment size for the allocation region
> >>   *
> >>   * Invoke to allocate memory for the PCI EPF register space.
> >>   */
> >> -void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar)
> >> +void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
> >> +			  size_t align)
> >>  {
> >>  	void *space;
> >>  	struct device *dev = epf->epc->dev.parent;
> >> @@ -120,7 +122,11 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar)
> >>  
> >>  	if (size < 128)
> >>  		size = 128;
> >> -	size = roundup_pow_of_two(size);
> >> +
> >> +	if (align)
> >> +		size = ALIGN(size, align);
> >> +	else
> >> +		size = roundup_pow_of_two(size);
> >>  
> >>  	space = dma_alloc_coherent(dev, size, &phys_addr, GFP_KERNEL);
> >>  	if (!space) {
> >> diff --git a/include/linux/pci-epc.h b/include/linux/pci-epc.h
> >> index c3ffa3917f88..f641badc2c61 100644
> >> --- a/include/linux/pci-epc.h
> >> +++ b/include/linux/pci-epc.h
> >> @@ -109,6 +109,7 @@ struct pci_epc {
> >>   * @reserved_bar: bitmap to indicate reserved BAR unavailable to function driver
> >>   * @bar_fixed_64bit: bitmap to indicate fixed 64bit BARs
> >>   * @bar_fixed_size: Array specifying the size supported by each BAR
> >> + * @align: alignment size required for BAR buffer allocation
> >>   */
> >>  struct pci_epc_features {
> >>  	unsigned int	linkup_notifier : 1;
> >> @@ -117,6 +118,7 @@ struct pci_epc_features {
> >>  	u8	reserved_bar;
> >>  	u8	bar_fixed_64bit;
> >>  	u64	bar_fixed_size[BAR_5 + 1];
> >> +	size_t	align;
> >>  };
> >>  
> >>  #define to_pci_epc(device) container_of((device), struct pci_epc, dev)
> >> diff --git a/include/linux/pci-epf.h b/include/linux/pci-epf.h
> >> index ec02f58758c8..2d6f07556682 100644
> >> --- a/include/linux/pci-epf.h
> >> +++ b/include/linux/pci-epf.h
> >> @@ -149,7 +149,8 @@ void pci_epf_destroy(struct pci_epf *epf);
> >>  int __pci_epf_register_driver(struct pci_epf_driver *driver,
> >>  			      struct module *owner);
> >>  void pci_epf_unregister_driver(struct pci_epf_driver *driver);
> >> -void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar);
> >> +void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
> >> +			  size_t align);
> >>  void pci_epf_free_space(struct pci_epf *epf, void *addr, enum pci_barno bar);
> >>  int pci_epf_bind(struct pci_epf *epf);
> >>  void pci_epf_unbind(struct pci_epf *epf);
> >> -- 
> >> 2.17.1
> >>

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