linux-kernel - [PATCH v4 09/25] PCI: histb: Remove redundant error fabrication when device read fails

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Message-Id: <7da7ea760abc5f85cad6e9b0d3e59eebd93f50d3.1637243717.git.naveennaidu479@gmail.com>
Date:   Thu, 18 Nov 2021 19:33:19 +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, Shawn Guo <shawn.guo@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>
Subject: [PATCH v4 09/25] PCI: histb: 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/dwc/pcie-histb.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-histb.c b/drivers/pci/controller/dwc/pcie-histb.c
index 86f9d16c50d7..410555dccb6d 100644
--- a/drivers/pci/controller/dwc/pcie-histb.c
+++ b/drivers/pci/controller/dwc/pcie-histb.c
@@ -127,10 +127,8 @@ static int histb_pcie_rd_own_conf(struct pci_bus *bus, unsigned int devfn,
 {
 	struct dw_pcie *pci = to_dw_pcie_from_pp(bus->sysdata);

-	if (PCI_SLOT(devfn)) {
-		*val = ~0;
+	if (PCI_SLOT(devfn))
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}

 	*val = dw_pcie_read_dbi(pci, where, size);
 	return PCIBIOS_SUCCESSFUL;
-- 
2.25.1