linux-kernel - Re: [PATCH v2 01/24] PCI: Add PCI_ERROR_RESPONSE and it's related definitions

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Date:   Wed, 20 Oct 2021 08:24:30 -0500
From:   Rob Herring <robh@...nel.org>
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
Subject: Re: [PATCH v2 01/24] PCI: Add PCI_ERROR_RESPONSE and it's related
 definitions

On Fri, Oct 15, 2021 at 07:58:16PM +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.
> 
> 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@...gle.com>
> Signed-off-by: Naveen Naidu <naveennaidu479@...il.com>
> ---
>  include/linux/pci.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index cd8aa6fce204..928c589bb5c4 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))

No reason for val to be a pointer.

Also, macro parameters need () around them. val could be an expression 
like 'ptr + 1' which would blow up for example.

> +
>  /*
>   * 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
> 
>