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: Thu, 11 Apr 2019 16:32:39 +0100

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.

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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