linux-kernel - Re: [PATCH v3 20/26] PCI: dwc: Fix dw_pcie_ep_find_capability to return correct capability offset

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Date:   Sat, 13 Apr 2019 10:44:37 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Rob Herring <robh+dt@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Murali Karicheri <m-karicheri2@...com>,
        Jingoo Han <jingoohan1@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-arm-kernel@...s.com,
        Minghuan Lian <minghuan.Lian@....com>,
        Mingkai Hu <mingkai.hu@....com>, Roy Zang <roy.zang@....com>,
        Jesper Nilsson <jesper.nilsson@...s.com>
Subject: Re: [PATCH v3 20/26] PCI: dwc: Fix dw_pcie_ep_find_capability to
 return correct capability offset

On Mon, Mar 25, 2019 at 03:09:41PM +0530, Kishon Vijay Abraham I wrote:
> commit beb4641a787df79a ("PCI: dwc: Add MSI-X callbacks handler") while
> adding MSI-X callback handler, introduced dw_pcie_ep_find_capability and
> __dw_pcie_ep_find_next_cap for finding the MSI and MSIX capability.
> 
> However if MSI or MSIX capability is the last capability (i.e there are
> no additional items in the capabilities list and the Next Capability
> Pointer is set to '0'), __dw_pcie_ep_find_next_cap will return '0'
> even though MSI or MSIX capability may be present. This is because of
> incorrect ordering of "next_cap_ptr" check. Fix it here.

Nice fix.  It looks like dw_pcie_ep_find_capability() is currently
only used for MSI and MSI-X, but IIUC, it *could* be used for any
capability, so this commit message seems a little too specific.

It would be slightly less confusing if beb4641a787d ("PCI: dwc: Add
MSI-X callbacks handler") had been split into a commit that added the
general-purpose dw_pcie_ep_find_capability() and a commit that used it
for MSI and MSI-X, but obviously we can't change history.

> Fixes: beb4641a787df79a142 ("PCI: dwc: Add MSI-X callbacks handler")

These commit references are longer than necessary (and different -
19-char SHA1 here and 16 chars above).  I typically use 12 chars via

  gsr is aliased to `git --no-pager show -s --abbrev-commit --abbrev=12 --pretty=format:"%h (\"%s\")%n"'


> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
> ---
>  drivers/pci/controller/dwc/pcie-designware-ep.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index dc6a4bbd3ace..74477ad7467f 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -46,16 +46,19 @@ static u8 __dw_pcie_ep_find_next_cap(struct dw_pcie *pci, u8 cap_ptr,
>  	u8 cap_id, next_cap_ptr;
>  	u16 reg;
>  
> +	if (!cap_ptr)
> +		return 0;
> +
>  	reg = dw_pcie_readw_dbi(pci, cap_ptr);
> -	next_cap_ptr = (reg & 0xff00) >> 8;
>  	cap_id = (reg & 0x00ff);
>  
> -	if (!next_cap_ptr || cap_id > PCI_CAP_ID_MAX)
> +	if (cap_id > PCI_CAP_ID_MAX)
>  		return 0;
>  
>  	if (cap_id == cap)
>  		return cap_ptr;
>  
> +	next_cap_ptr = (reg & 0xff00) >> 8;
>  	return __dw_pcie_ep_find_next_cap(pci, next_cap_ptr, cap);
>  }
>  
> @@ -67,9 +70,6 @@ static u8 dw_pcie_ep_find_capability(struct dw_pcie *pci, u8 cap)
>  	reg = dw_pcie_readw_dbi(pci, PCI_CAPABILITY_LIST);
>  	next_cap_ptr = (reg & 0x00ff);
>  
> -	if (!next_cap_ptr)
> -		return 0;
> -
>  	return __dw_pcie_ep_find_next_cap(pci, next_cap_ptr, cap);
>  }
>  
> -- 
> 2.17.1
>