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, Robert Richter <rric@kernel.org>,
        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 (moderated list:PCIE DRIVER FOR
        CAVIUM THUNDERX)
Subject: [PATCH v4 05/25] PCI: thunder: Remove redundant error fabrication when device read fails
Date:   Thu, 18 Nov 2021 19:33:15 +0530
Message-Id: <22f471b638276422926c49f3d42ac41bc7b28b3d.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-thunder-ecam.c | 46 ++++++++---------------
 drivers/pci/controller/pci-thunder-pem.c  |  4 +-
 2 files changed, 17 insertions(+), 33 deletions(-)

diff --git a/drivers/pci/controller/pci-thunder-ecam.c b/drivers/pci/controller/pci-thunder-ecam.c
index e9d5ca245f5e..b5bd10a62adb 100644
--- a/drivers/pci/controller/pci-thunder-ecam.c
+++ b/drivers/pci/controller/pci-thunder-ecam.c
@@ -41,10 +41,9 @@ static int handle_ea_bar(u32 e0, int bar, struct pci_bus *bus,
 	}
 	if (where_a == 0x4) {
 		addr = bus->ops->map_bus(bus, devfn, bar); /* BAR 0 */
-		if (!addr) {
-			*val = ~0;
+		if (!addr)
 			return PCIBIOS_DEVICE_NOT_FOUND;
-		}
+
 		v = readl(addr);
 		v &= ~0xf;
 		v |= 2; /* EA entry-1. Base-L */
@@ -56,10 +55,9 @@ static int handle_ea_bar(u32 e0, int bar, struct pci_bus *bus,
 		u32 barl_rb;
 
 		addr = bus->ops->map_bus(bus, devfn, bar); /* BAR 0 */
-		if (!addr) {
-			*val = ~0;
+		if (!addr)
 			return PCIBIOS_DEVICE_NOT_FOUND;
-		}
+
 		barl_orig = readl(addr + 0);
 		writel(0xffffffff, addr + 0);
 		barl_rb = readl(addr + 0);
@@ -72,10 +70,9 @@ static int handle_ea_bar(u32 e0, int bar, struct pci_bus *bus,
 	}
 	if (where_a == 0xc) {
 		addr = bus->ops->map_bus(bus, devfn, bar + 4); /* BAR 1 */
-		if (!addr) {
-			*val = ~0;
+		if (!addr)
 			return PCIBIOS_DEVICE_NOT_FOUND;
-		}
+
 		v = readl(addr); /* EA entry-3. Base-H */
 		set_val(v, where, size, val);
 		return PCIBIOS_SUCCESSFUL;
@@ -104,10 +101,8 @@ static int thunder_ecam_p2_config_read(struct pci_bus *bus, unsigned int devfn,
 	}
 
 	addr = bus->ops->map_bus(bus, devfn, where_a);
-	if (!addr) {
-		*val = ~0;
+	if (!addr)
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}
 
 	v = readl(addr);
 
@@ -135,10 +130,8 @@ static int thunder_ecam_config_read(struct pci_bus *bus, unsigned int devfn,
 	int where_a = where & ~3;
 
 	addr = bus->ops->map_bus(bus, devfn, 0xc);
-	if (!addr) {
-		*val = ~0;
+	if (!addr)
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}
 
 	v = readl(addr);
 
@@ -146,10 +139,8 @@ static int thunder_ecam_config_read(struct pci_bus *bus, unsigned int devfn,
 	cfg_type = (v >> 16) & 0x7f;
 
 	addr = bus->ops->map_bus(bus, devfn, 8);
-	if (!addr) {
-		*val = ~0;
+	if (!addr)
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}
 
 	class_rev = readl(addr);
 	if (class_rev == 0xffffffff)
@@ -176,10 +167,8 @@ static int thunder_ecam_config_read(struct pci_bus *bus, unsigned int devfn,
 	}
 
 	addr = bus->ops->map_bus(bus, devfn, 0);
-	if (!addr) {
-		*val = ~0;
+	if (!addr)
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}
 
 	vendor_device = readl(addr);
 	if (vendor_device == 0xffffffff)
@@ -196,10 +185,9 @@ static int thunder_ecam_config_read(struct pci_bus *bus, unsigned int devfn,
 		bool is_tns = (vendor_device == 0xa01f177d);
 
 		addr = bus->ops->map_bus(bus, devfn, 0x70);
-		if (!addr) {
-			*val = ~0;
+		if (!addr)
 			return PCIBIOS_DEVICE_NOT_FOUND;
-		}
+
 		/* E_CAP */
 		v = readl(addr);
 		has_msix = (v & 0xff00) != 0;
@@ -211,10 +199,9 @@ static int thunder_ecam_config_read(struct pci_bus *bus, unsigned int devfn,
 		}
 		if (where_a == 0xb0) {
 			addr = bus->ops->map_bus(bus, devfn, where_a);
-			if (!addr) {
-				*val = ~0;
+			if (!addr)
 				return PCIBIOS_DEVICE_NOT_FOUND;
-			}
+
 			v = readl(addr);
 			if (v & 0xff00)
 				pr_err("Bad MSIX cap header: %08x\n", v);
@@ -268,10 +255,9 @@ static int thunder_ecam_config_read(struct pci_bus *bus, unsigned int devfn,
 
 		if (where_a == 0x70) {
 			addr = bus->ops->map_bus(bus, devfn, where_a);
-			if (!addr) {
-				*val = ~0;
+			if (!addr)
 				return PCIBIOS_DEVICE_NOT_FOUND;
-			}
+
 			v = readl(addr);
 			if (v & 0xff00)
 				pr_err("Bad PCIe cap header: %08x\n", v);
diff --git a/drivers/pci/controller/pci-thunder-pem.c b/drivers/pci/controller/pci-thunder-pem.c
index 0660b9da204f..06a9855cb431 100644
--- a/drivers/pci/controller/pci-thunder-pem.c
+++ b/drivers/pci/controller/pci-thunder-pem.c
@@ -41,10 +41,8 @@ static int thunder_pem_bridge_read(struct pci_bus *bus, unsigned int devfn,
 	struct pci_config_window *cfg = bus->sysdata;
 	struct thunder_pem_pci *pem_pci = (struct thunder_pem_pci *)cfg->priv;
 
-	if (devfn != 0 || where >= 2048) {
-		*val = ~0;
+	if (devfn != 0 || where >= 2048)
 		return PCIBIOS_DEVICE_NOT_FOUND;
-	}
 
 	/*
 	 * 32-bit accesses only.  Write the address to the low order
-- 
2.25.1