From:   Naveen Naidu <naveennaidu479@gmail.com>
To:     bhelgaas@google.com
Cc:     Naveen Naidu <naveennaidu479@gmail.com>,
        linux-kernel-mentees@lists.linuxfoundation.org,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        skhan@linuxfoundation.org,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Rob Herring <robh@kernel.org>,
        =?UTF-8?q?Krzysztof=20Wilczy=C5=84ski?= <kw@linux.com>,
        linux-arm-kernel@lists.infradead.org
Subject: [PATCH v4 12/25] PCI: mvebu: Remove redundant error fabrication when device read fails
Date:   Thu, 18 Nov 2021 19:33:22 +0530
Message-Id: <f30264b137b1282ffda34d336e8060bb13d60b98.1637243717.git.naveennaidu479@gmail.com>
In-Reply-To: <cover.1637243717.git.naveennaidu479@gmail.com>
References: <cover.1637243717.git.naveennaidu479@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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@gmail.com>
---
 drivers/pci/controller/pci-mvebu.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/controller/pci-mvebu.c b/drivers/pci/controller/pci-mvebu.c
index ed13e81cd691..70a96af8cd2f 100644
--- a/drivers/pci/controller/pci-mvebu.c
+++ b/drivers/pci/controller/pci-mvebu.c
@@ -653,20 +653,16 @@ static int mvebu_pcie_rd_conf(struct pci_bus *bus, u32 devfn, int where,
 	int ret;
 
 	port = mvebu_pcie_find_port(pcie, bus, devfn);
-	if (!port) {
-		*val = 0xffffffff;
+	if (!port)
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}
 
 	/* Access the emulated PCI-to-PCI bridge */
 	if (bus->number == 0)
 		return pci_bridge_emul_conf_read(&port->bridge, where,
 						 size, val);
 
-	if (!mvebu_pcie_link_up(port)) {
-		*val = 0xffffffff;
+	if (!mvebu_pcie_link_up(port))
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}
 
 	/* Access the real PCIe interface */
 	ret = mvebu_pcie_hw_rd_conf(port, bus, devfn,
-- 
2.25.1