linux-kernel - [PATCH v2 11/24] PCI: aardvark: Remove redundant error fabrication when device read fails

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Date:   Fri, 15 Oct 2021 20:08:52 +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,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Pali Rohár <pali@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-arm-kernel@...ts.infradead.org (moderated list:PCI DRIVER FOR
        AARDVARK (Marvell Armada 3700))
Subject: [PATCH v2 11/24] PCI: aardvark: 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.

Signed-off-by: Naveen Naidu <naveennaidu479@...il.com>
---
 drivers/pci/controller/pci-aardvark.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
index 596ebcfcc82d..1af772c76d06 100644
--- a/drivers/pci/controller/pci-aardvark.c
+++ b/drivers/pci/controller/pci-aardvark.c
@@ -893,10 +893,8 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
 	u32 reg;
 	int ret;
 
-	if (!advk_pcie_valid_device(pcie, bus, devfn)) {
-		*val = 0xffffffff;
+	if (!advk_pcie_valid_device(pcie, bus, devfn))
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}
 
 	if (pci_is_root_bus(bus))
 		return pci_bridge_emul_conf_read(&pcie->bridge, where,
@@ -920,7 +918,6 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
 			*val = CFG_RD_CRS_VAL;
 			return PCIBIOS_SUCCESSFUL;
 		}
-		*val = 0xffffffff;
 		return PCIBIOS_SET_FAILED;
 	}
 
@@ -955,16 +952,13 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
 			*val = CFG_RD_CRS_VAL;
 			return PCIBIOS_SUCCESSFUL;
 		}
-		*val = 0xffffffff;
 		return PCIBIOS_SET_FAILED;
 	}
 
 	/* Check PIO status and get the read result */
 	ret = advk_pcie_check_pio_status(pcie, allow_crs, val);
-	if (ret < 0) {
-		*val = 0xffffffff;
+	if (ret < 0)
 		return PCIBIOS_SET_FAILED;
-	}
 
 	if (size == 1)
 		*val = (*val >> (8 * (where & 3))) & 0xff;
-- 
2.25.1