PCI: endpoint: Improve pci_epf_alloc_space() API

pci_epf_alloc_space() already performs checks on the requested BAR size,
and will allocate and set epf_bar->size to a size higher than the
requested BAR size if some constraint deems it necessary.

However, there are additional checks done in the function drivers like
pci-epf-test.c, other than the existing checks in this API.

And similar checks are proposed to other endpoint function drivers, see:
https://lore.kernel.org/linux-pci/20240108151015.2030469-1-Frank.Li@nxp.com

Having these checks scattered over different locations in multiple EPF
drivers is not maintainable and makes the code hard to follow.

Since pci_epf_alloc_space() already performs roundups and some checks,
let's move the additional checks from pci-epf-test.c to
pci_epf_alloc_space().

This makes the API more robust and also offloads the checks from the
function drivers.
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20240207213922.1796533-3-cassel@kernel.org
[mani: reworded commit message and fixed uninitialized 'dev' pointer issue]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

drivers/pci/endpoint/pci-epf-core.c

@@ -260,6 +260,7 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
 			  const struct pci_epc_features *epc_features,
 			  enum pci_epc_interface_type type)
 {
+	u64 bar_fixed_size = epc_features->bar_fixed_size[bar];
 	size_t align = epc_features->align;
 	struct pci_epf_bar *epf_bar;
 	dma_addr_t phys_addr;
@@ -270,6 +271,14 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
 	if (size < 128)
 		size = 128;
 
+	if (bar_fixed_size && size > bar_fixed_size) {
+		dev_err(&epf->dev, "requested BAR size is larger than fixed size\n");
+		return NULL;
+	}
+
+	if (bar_fixed_size)
+		size = bar_fixed_size;
+
 	if (align)
 		size = ALIGN(size, align);
 	else