linux-kernel - [PATCH v3 14/25] PCI: rcar: Remove redundant error fabrication when device read fails

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Message-Id: <29e534503de9502e4a30a1cb970f72c20243cc7e.1634825082.git.naveennaidu479@gmail.com>
Date:   Thu, 21 Oct 2021 20:37:39 +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,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Marek Vasut <marek.vasut+renesas@...il.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-renesas-soc@...r.kernel.org (open list:PCI DRIVER FOR RENESAS
        R-CAR)
Subject: [PATCH v3 14/25] PCI: rcar: 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: Geert Uytterhoeven <geert+renesas@...der.be>
Signed-off-by: Naveen Naidu <naveennaidu479@...il.com>
---
 drivers/pci/controller/pcie-rcar-host.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/pci/controller/pcie-rcar-host.c b/drivers/pci/controller/pcie-rcar-host.c
index 8f3131844e77..1324cb984ed5 100644
--- a/drivers/pci/controller/pcie-rcar-host.c
+++ b/drivers/pci/controller/pcie-rcar-host.c
@@ -161,10 +161,8 @@ static int rcar_pcie_read_conf(struct pci_bus *bus, unsigned int devfn,
 
 	ret = rcar_pcie_config_access(host, RCAR_PCI_ACCESS_READ,
 				      bus, devfn, where, val);
-	if (ret != PCIBIOS_SUCCESSFUL) {
-		*val = 0xffffffff;
+	if (ret != PCIBIOS_SUCCESSFUL)
 		return ret;
-	}
 
 	if (size == 1)
 		*val = (*val >> (BITS_PER_BYTE * (where & 3))) & 0xff;
-- 
2.25.1