linux-kernel - Re: [PATCH 16/22] PCI: pciehp: Use RESPONSE_IS_PCI

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Date:   Mon, 11 Oct 2021 21:47:40 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Naveen Naidu <naveennaidu479@...il.com>
Cc:     bhelgaas@...gle.com,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Amey Narkhede <ameynarkhede03@...il.com>
Subject: Re: [PATCH 16/22] PCI: pciehp: Use RESPONSE_IS_PCI_ERROR() to check
 read from hardware

On Mon, Oct 11, 2021 at 11:37:33PM +0530, Naveen Naidu wrote:
> 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 RESPONSE_IS_PCI_ERROR() to check the response we get when we read
> data from hardware.

Actually what happens is that PCI read transactions *time out*,
so the host controller fabricates a response.

By contrast, a PCI *error* usually denotes an Uncorrectable or
Correctable Error as specified in section 6.2.2 of the PCIe Base Spec.

Thus something like RESPONSE_IS_PCI_TIMEOUT() or IS_PCI_TIMEOUT() would
probably be more appropriate.  I'll leave the exact bikeshed color for
others to decide. :-)


> Signed-off-by: Naveen Naidu <naveennaidu479@...il.com>
> ---
>  drivers/pci/hotplug/pciehp_hpc.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)

Acked-by: Lukas Wunner <lukas@...ner.de>