linux-kernel - Re: [PATCH] PCI: qcom: Fix warning generated due to the incorrect data type

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Message-ID: <20211130033614.GA2721688@bhelgaas>
Date:   Mon, 29 Nov 2021 21:36:14 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     lorenzo.pieralisi@....com, bhelgaas@...gle.com,
        svarbanov@...sol.com, bjorn.andersson@...aro.org, robh@...nel.org,
        linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] PCI: qcom: Fix warning generated due to the incorrect
 data type

On Wed, Nov 24, 2021 at 07:34:24PM +0530, Manivannan Sadhasivam wrote:
> Fix the below sparse warning due to the use of incorrect initializer
> data type (u16) for bdf_be variable that receives the return value of
> cpu_to_be16(). The correct type should be __be16.

I think the patch looks OK, but the reason to change this is not to
"fix the warning".  The reason is to fix the *problem*, i.e.,
cpu_to_be16() returns "__be16", which is incompatible with "u16".

The warning is only a helpful hint, and should not be part of the
subject line.  "cpu_to_be16" or "iommu-map" would be much more
useful information in the subject.

I'm also curious why pcie-qcom.c is the only driver that does this.
"iommu-map" is not specific to qcom, but no other drivers do similar
things with it.

> sparse warnings: (new ones prefixed by >>)
> >> drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse: sparse: incorrect type in initializer (different base types) @@     expected unsigned short [usertype] bdf_be @@     got restricted __be16 [usertype] @@
>    drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     expected unsigned short [usertype] bdf_be
>    drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     got restricted __be16 [usertype]
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 8a7a300163e5..6c3b034e9946 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -1312,7 +1312,7 @@ static int qcom_pcie_config_sid_sm8250(struct qcom_pcie *pcie)
>  
>  	/* Look for an available entry to hold the mapping */
>  	for (i = 0; i < nr_map; i++) {
> -		u16 bdf_be = cpu_to_be16(map[i].bdf);
> +		__be16 bdf_be = cpu_to_be16(map[i].bdf);
>  		u32 val;
>  		u8 hash;
>  
> -- 
> 2.25.1
>