Hello Jerome,
On Mon, Apr 07, 2025 at 04:39:08PM +0200, Jerome Brunet wrote:
> When trying to allocate space for an endpoint function on a BAR with a
> fixed size, the size saved in the 'struct pci_epf_bar' should be the fixed
> size. This is expected by pci_epc_set_bar().
>
> However, if the fixed_size is smaller that the alignment, the size saved
> in the 'struct pci_epf_bar' matches the alignment and it is a problem for
> pci_epc_set_bar().
>
> To solve this, continue to allocate space that match the iATU alignment
> requirement but save the size that matches what is present in the BAR.
>
> Fixes: 2a9a801620ef ("PCI: endpoint: Add support to specify alignment for buffers allocated to BARs")
> Signed-off-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx>
> ---
> drivers/pci/endpoint/pci-epf-core.c | 25 +++++++++++++++++--------
> 1 file changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c
> index b7deb0ee1760b23a24f49abf3baf53ea2f273476..fb902b751e1c965c902c5199d57969ae0a757c2e 100644
> --- a/drivers/pci/endpoint/pci-epf-core.c
> +++ b/drivers/pci/endpoint/pci-epf-core.c
> @@ -225,6 +225,7 @@ void pci_epf_free_space(struct pci_epf *epf, void *addr, enum pci_barno bar,
> struct device *dev;
> struct pci_epf_bar *epf_bar;
> struct pci_epc *epc;
> + size_t size;
>
> if (!addr)
> return;
> @@ -237,9 +238,12 @@ void pci_epf_free_space(struct pci_epf *epf, void *addr, enum pci_barno bar,
> epf_bar = epf->sec_epc_bar;
> }
>
> + size = epf_bar[bar].size;
> + if (epc_features->align)
> + size = ALIGN(size, epc_features->align);
Personally, I think that you should just save the aligned_size / mem_size /
backing_mem_size as a new struct member, as that avoids the risk that someone
later modifies pci_epf_alloc_space() but forgets to update
pci_epf_free_space() accordingly.
But I will leave the decision to the PCI endpoint maintainers.
Kind regards,
Niklas
> +
> dev = epc->dev.parent;
> - dma_free_coherent(dev, epf_bar[bar].size, addr,
> - epf_bar[bar].phys_addr);
> + dma_free_coherent(dev, size, addr, epf_bar[bar].phys_addr);
>
> epf_bar[bar].phys_addr = 0;
> epf_bar[bar].addr = NULL;
> @@ -266,7 +270,7 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
> enum pci_epc_interface_type type)
> {
> u64 bar_fixed_size = epc_features->bar[bar].fixed_size;
> - size_t align = epc_features->align;
> + size_t aligned_size, align = epc_features->align;
> struct pci_epf_bar *epf_bar;
> dma_addr_t phys_addr;
> struct pci_epc *epc;
> @@ -287,12 +291,17 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
> return NULL;
> }
> size = bar_fixed_size;
> + } else {
> + /* BAR size must be power of two */
> + size = roundup_pow_of_two(size);
> }
>
> - if (align)
> - size = ALIGN(size, align);
> - else
> - size = roundup_pow_of_two(size);
> + /*
> + * Allocate enough memory to accommodate the iATU alignment requirement.
> + * In most cases, this will be the same as .size but it might be different
> + * if, for example, the fixed size of a BAR is smaller than align
> + */
> + aligned_size = align ? ALIGN(size, align) : size;
>
> if (type == PRIMARY_INTERFACE) {
> epc = epf->epc;
> @@ -303,7 +312,7 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
> }
>
> dev = epc->dev.parent;
> - space = dma_alloc_coherent(dev, size, &phys_addr, GFP_KERNEL);
> + space = dma_alloc_coherent(dev, aligned_size, &phys_addr, GFP_KERNEL);
> if (!space) {
> dev_err(dev, "failed to allocate mem space\n");
> return NULL;
>
> --
> 2.47.2
>
