linux-kernel - [PATCH v3 04/25] PCI: Remove redundant error fabrication when device read fails

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Date:   Thu, 21 Oct 2021 20:37:29 +0530
From:   Naveen Naidu <naveennaidu479@...il.com>
To:     bhelgaas@...gle.com
Cc:     Naveen Naidu <naveennaidu479@...il.com>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        skhan@...uxfoundation.org, Rob Herring <robh@...nel.org>
Subject: [PATCH v3 04/25] PCI: Remove redundant error fabrication when device read fails

An MMIO read from a PCI device that doesn't exist or doesn't respond
causes a PCI error. There's no real data to return to satisfy the
CPU read, so most hardware fabricates ~0 data.

The host controller drivers sets the error response values (~0) and
returns an error when faulty hardware read occurs. But the error
response value (~0) is already being set in PCI_OP_READ and
PCI_USER_READ_CONFIG whenever a read by host controller driver fails.

Thus, it's no longer necessary for the host controller drivers to
fabricate any error response.

This helps unify PCI error response checking and make error check
consistent and easier to find.

Reviewed-by: Rob Herring <robh@...nel.org>
Signed-off-by: Naveen Naidu <naveennaidu479@...il.com>
---
 drivers/pci/access.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index a6bcbad04d89..2705a4412e69 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -83,10 +83,8 @@ int pci_generic_config_read(struct pci_bus *bus, unsigned int devfn,
 	void __iomem *addr;

 	addr = bus->ops->map_bus(bus, devfn, where);
-	if (!addr) {
-		*val = ~0;
+	if (!addr)
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}

 	if (size == 1)
 		*val = readb(addr);
@@ -125,10 +123,8 @@ int pci_generic_config_read32(struct pci_bus *bus, unsigned int devfn,
 	void __iomem *addr;

 	addr = bus->ops->map_bus(bus, devfn, where & ~0x3);
-	if (!addr) {
-		*val = ~0;
+	if (!addr)
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}

 	*val = readl(addr);

-- 
2.25.1