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Date:   Thu, 21 Oct 2021 18:08:38 +0200
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     Naveen Naidu <naveennaidu479@gmail.com>
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Subject: Re: [PATCH v3 01/25] PCI: Add PCI_ERROR_RESPONSE and it's related
 definitions
Message-ID: <20211021160838.r7t7fmmeseaecfac@pali>
References: <cover.1634825082.git.naveennaidu479@gmail.com>
 <f7960a4dee0e417eedd7d2e031d04ac9016c6686.1634825082.git.naveennaidu479@gmail.com>
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On Thursday 21 October 2021 20:37:26 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.
> 
> Add a PCI_ERROR_RESPONSE definition for that and use it where
> appropriate to make these checks consistent and easier to find.
> 
> Also add helper definitions SET_PCI_ERROR_RESPONSE and
> RESPONSE_IS_PCI_ERROR to make the code more readable.
> 
> Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Naveen Naidu <naveennaidu479@gmail.com>

Reviewed-by: Pali Rohár <pali@kernel.org>

> ---
>  include/linux/pci.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index cd8aa6fce204..689c8277c584 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -154,6 +154,15 @@ enum pci_interrupt_pin {
>  /* The number of legacy PCI INTx interrupts */
>  #define PCI_NUM_INTX	4
>  
> +/*
> + * Reading from a device that doesn't respond typically returns ~0.  A
> + * successful read from a device may also return ~0, so you need additional
> + * information to reliably identify errors.
> + */
> +#define PCI_ERROR_RESPONSE     (~0ULL)
> +#define SET_PCI_ERROR_RESPONSE(val)    (*(val) = ((typeof(*(val))) PCI_ERROR_RESPONSE))
> +#define RESPONSE_IS_PCI_ERROR(val) ((val) == ((typeof(val)) PCI_ERROR_RESPONSE))
> +
>  /*
>   * pci_power_t values must match the bits in the Capabilities PME_Support
>   * and Control/Status PowerState fields in the Power Management capability.
> -- 
> 2.25.1
>