linux-kernel - Re: [PATCH v2 06/24] PCI: iproc: Remove redundant error fabrication when device read fails

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Message-ID: <a3f9ab4e-094b-437e-5c7b-7f72c50b3ff5@broadcom.com>
Date:   Fri, 15 Oct 2021 09:49:01 -0700
From:   Ray Jui <ray.jui@...adcom.com>
To:     Naveen Naidu <naveennaidu479@...il.com>, bhelgaas@...gle.com
Cc:     linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        "maintainer:BROADCOM IPROC ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "moderated list:BROADCOM IPROC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 06/24] PCI: iproc: Remove redundant error fabrication
 when device read fails



On 10/15/2021 7:38 AM, 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.
> 
> 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@...il.com>
> ---
>  drivers/pci/controller/pcie-iproc.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/pcie-iproc.c b/drivers/pci/controller/pcie-iproc.c
> index 30ac5fbefbbf..e3d86416a4fb 100644
> --- a/drivers/pci/controller/pcie-iproc.c
> +++ b/drivers/pci/controller/pcie-iproc.c
> @@ -659,10 +659,8 @@ static int iproc_pci_raw_config_read32(struct iproc_pcie *pcie,
>  	void __iomem *addr;
>  
>  	addr = iproc_pcie_map_cfg_bus(pcie, 0, devfn, where & ~0x3);
> -	if (!addr) {
> -		*val = ~0;
> +	if (!addr)
>  		return PCIBIOS_DEVICE_NOT_FOUND;
> -	}
>  
>  	*val = readl(addr);
>  
> 

I think it would be helpful if you include us in the review of the PCI
core code change (pci.h and access.c) so we get the right context to
review this change at the individual driver level.

The driver change looks fine to me, as long as the change in the core is
reviewed and approved.

Thanks,

Ray

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