PCI: endpoint: Improve pci_epc_mem_alloc_addr()

There is no point in attempting to allocate memory from an endpoint
controller memory window if the requested size is larger than the memory
window size. Add a check to skip bitmap_find_free_region() calls for
such case. This check can be done without the mem->lock mutex held as
memory window sizes are constant and never modified at runtime.
Also change the final return to return NULL to simplify the code.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20241012113246.95634-3-dlemoal@kernel.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Author: damien-lemoal

drivers/pci/endpoint/pci-epc-mem.c

@@ -178,7 +178,7 @@ EXPORT_SYMBOL_GPL(pci_epc_mem_exit);
 void __iomem *pci_epc_mem_alloc_addr(struct pci_epc *epc,
 				     phys_addr_t *phys_addr, size_t size)
 {
-	void __iomem *virt_addr = NULL;
+	void __iomem *virt_addr;
 	struct pci_epc_mem *mem;
 	unsigned int page_shift;
 	size_t align_size;
@@ -188,10 +188,13 @@ void __iomem *pci_epc_mem_alloc_addr(struct pci_epc *epc,
 
 	for (i = 0; i < epc->num_windows; i++) {
 		mem = epc->windows[i];
-		mutex_lock(&mem->lock);
+		if (size > mem->window.size)
+			continue;
+
 		align_size = ALIGN(size, mem->window.page_size);
 		order = pci_epc_mem_get_order(mem, align_size);
 
+		mutex_lock(&mem->lock);
 		pageno = bitmap_find_free_region(mem->bitmap, mem->pages,
 						 order);
 		if (pageno >= 0) {
@@ -211,7 +214,7 @@ void __iomem *pci_epc_mem_alloc_addr(struct pci_epc *epc,
 		mutex_unlock(&mem->lock);
 	}
 
-	return virt_addr;
+	return NULL;
 }
 EXPORT_SYMBOL_GPL(pci_epc_mem_alloc_addr);