PCI: endpoint: Allow EPF drivers to configure the size of Resizable BARs

A resizable BAR is different from a normal BAR in a few ways:

  - The minimum size of a resizable BAR is 1 MB.
  - Each BAR that is resizable has a Capability and Control register in
    the Resizable BAR Capability structure.

These registers contain the supported sizes and the currently selected
size of a resizable BAR.

The supported sizes is a bitmap of the supported sizes. The selected size
is a single value that is equal to one of the supported sizes.

A resizable BAR thus has to be configured differently than a
BAR_PROGRAMMABLE BAR, which usually sets the BAR size/mask in a vendor
specific way.

The PCI endpoint framework currently does not support resizable BARs.

Add a BAR type BAR_RESIZABLE, so that an EPC driver can support resizable
BARs properly.

Note that the pci_epc_set_bar() API takes a struct pci_epf_bar which tells
the EPC driver how it wants to configure the BAR.

struct pci_epf_bar only has a single size struct member.

This means that an EPC driver will only be able to set a single supported
size. This is perfectly fine, as we do not need the complexity of allowing
a host to change the size of the BAR. If someone ever wants to support
resizing a resizable BAR, the pci_epc_set_bar() API can be extended in the
future.

With these changes, we allow an EPF driver to configure the size of
Resizable BARs, rather than forcing them to a 1 MB size.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20250131182949.465530-10-cassel@kernel.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

3 files changed, 12 insertions, 0 deletions

diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
index 9e9ca5f8e8f8..10dfc716328e 100644
--- a/drivers/pci/endpoint/pci-epc-core.c
+++ b/drivers/pci/endpoint/pci-epc-core.c
@@ -609,6 +609,10 @@ int pci_epc_set_bar(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
 	if (!epc_features)
 		return -EINVAL;
 
+	if (epc_features->bar[bar].type == BAR_RESIZABLE &&
+	    (epf_bar->size < SZ_1M || (u64)epf_bar->size > (SZ_128G * 1024)))
+		return -EINVAL;
+
 	if (epc_features->bar[bar].type == BAR_FIXED &&
 	    (epc_features->bar[bar].fixed_size != epf_bar->size))
 		return -EINVAL;
diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c
index 50bc2892a36c..394395c7f8de 100644
--- a/drivers/pci/endpoint/pci-epf-core.c
+++ b/drivers/pci/endpoint/pci-epf-core.c
@@ -274,6 +274,10 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
 	if (size < 128)
 		size = 128;
 
+	/* According to PCIe base spec, min size for a resizable BAR is 1 MB. */
+	if (epc_features->bar[bar].type == BAR_RESIZABLE && size < SZ_1M)
+		size = SZ_1M;
+
 	if (epc_features->bar[bar].type == BAR_FIXED && bar_fixed_size) {
 		if (size > bar_fixed_size) {
 			dev_err(&epf->dev,
diff --git a/include/linux/pci-epc.h b/include/linux/pci-epc.h
index e818e3fdcded..91ce39dc0fd4 100644
--- a/include/linux/pci-epc.h
+++ b/include/linux/pci-epc.h
@@ -188,11 +188,15 @@ struct pci_epc {
  * enum pci_epc_bar_type - configurability of endpoint BAR
  * @BAR_PROGRAMMABLE: The BAR mask can be configured by the EPC.
  * @BAR_FIXED: The BAR mask is fixed by the hardware.
+ * @BAR_RESIZABLE: The BAR implements the PCI-SIG Resizable BAR Capability.
+ *		   NOTE: An EPC driver can currently only set a single supported
+ *		   size.
  * @BAR_RESERVED: The BAR should not be touched by an EPF driver.
  */
 enum pci_epc_bar_type {
 	BAR_PROGRAMMABLE = 0,
 	BAR_FIXED,
+	BAR_RESIZABLE,
 	BAR_RESERVED,
 };