On Monday 11 October 2021 23:55:35 Naveen Naidu wrote:

On 11/10, Pali Rohár wrote:

quoted

On Monday 11 October 2021 23:26:33 Naveen Naidu wrote:

quoted

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.

Use SET_PCI_ERROR_RESPONSE() to set the error response, when a faulty
read occurs.

This helps unify PCI error response checking and make error check
consistent and easier to find.

Compile tested only.

Signed-off-by: Naveen Naidu <redacted>
---
 drivers/pci/controller/pci-aardvark.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
index 596ebcfcc82d..dc2f820ef55f 100644
--- a/drivers/pci/controller/pci-aardvark.c
+++ b/drivers/pci/controller/pci-aardvark.c

@@ -894,7 +894,7 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
 	int ret;
 
 	if (!advk_pcie_valid_device(pcie, bus, devfn)) {
-		*val = 0xffffffff;
+		SET_PCI_ERROR_RESPONSE(val);

Hello! Now I'm looking at this macro, and should not it depends on
"size" argument? If doing 8-bit or 16-bit read operation then should not
it rather sets only low 8 bits or low 16 bits to ones?

Hello o/, Thank you for the review.

Yes! you are right that it should indeed depend on the "size" argument.
And that is what the SET_PCI_ERROR_RESPONSE macro does. The macro is
defined as:

  #define PCI_ERROR_RESPONSE           (~0ULL)
  #define SET_PCI_ERROR_RESPONSE(val)  (*val = ((typeof(*val))PCI_ERROR_RESPONSE))

The macro was part of "Patch 1/22" and is present here [1]. Apologies if
I added the receipient incorrectly.

[1]:
https://lore.kernel.org/linux-pci/d8e423386aad3d78bca575a7521b138508638e3b.1633972263.git.naveennaidu479@gmail.com/T/#m37295a0dcfe0d7e0f67efce3633efd7b891949c4 (local)

IIUC, the typeof(*val) helps in setting the value according to the size
of the argument.

Please let me know if my understanding is wrong.

Hello! I mean "size" function argument which is passed as variable.

Function itself is declared as:

static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn, int where, int size, u32 *val);

And in "size" argument is stored number of bytes, kind of read operation
(read byte, read word, read dword). In *val is then stored read value.
For byte operation, just low 8 bits in *val variable are set.

Because *val is u32 it means that typeof(*val) is always 4 independently
of the "size" argument.

For example other project U-Boot has also pci-aardvark.c driver and
U-Boot has for (probably same) purpose pci_get_ff() macro, see:
https://source.denx.de/u-boot/u-boot/-/blob/v2021.10/drivers/pci/pci-aardvark.c#L367

I'm not saying if current approach to always sets 0xffffffff
(independently of "size" argument) is correct or not as I do not know
it too! I'm just giving example that this PCI code has very similar
implementation of other project (U-Boot) which sets number of ones based
on the size argument.

So probably something for other people to decide.

Anyway, I very like this your idea to have a macro which purpose is to
explicitly indicate error during config read operation! And to unify all
drivers to use same style for signalling config read error.

quoted

quoted

 		return PCIBIOS_DEVICE_NOT_FOUND;
 	}
 

@@ -920,7 +920,7 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
 			*val = CFG_RD_CRS_VAL;
 			return PCIBIOS_SUCCESSFUL;
 		}
-		*val = 0xffffffff;
+		SET_PCI_ERROR_RESPONSE(val);
 		return PCIBIOS_SET_FAILED;
 	}
 

@@ -955,14 +955,14 @@ static int advk_pcie_rd_conf(struct pci_bus *bus, u32 devfn,
 			*val = CFG_RD_CRS_VAL;
 			return PCIBIOS_SUCCESSFUL;
 		}
-		*val = 0xffffffff;
+		SET_PCI_ERROR_RESPONSE(val);
 		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;
+		SET_PCI_ERROR_RESPONSE(val);
 		return PCIBIOS_SET_FAILED;
 	}
 

-- 
2.25.1

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