Re: [PATCH] PCI: Mediatek: Use resource_size function on resource object

[Bjorn Helgaas]

On Wed, Jan 02, 2019 at 02:03:53PM +0800, honghui.zhang@xxxxxxxxxxxx wrote:
> From: Honghui Zhang <honghui.zhang@xxxxxxxxxxxx>
> 
> drivers/pci/pcie-mediatek.c:720:13-16: WARNING: Suspicious code. resource_size is maybe missing with mem
> 
> Generated by: scripts/coccinelle/api/resource_size.cocci
> 
> Signed-off-by: Honghui Zhang <honghui.zhang@xxxxxxxxxxxx>
> ---
>  drivers/pci/controller/pcie-mediatek.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
> index e307166..0168376 100644
> --- a/drivers/pci/controller/pcie-mediatek.c
> +++ b/drivers/pci/controller/pcie-mediatek.c
> @@ -654,7 +654,6 @@ static int mtk_pcie_startup_port_v2(struct mtk_pcie_port *port)
>  	struct resource *mem = &pcie->mem;
>  	const struct mtk_pcie_soc *soc = port->pcie->soc;
>  	u32 val;
> -	size_t size;
>  	int err;
>  
>  	/* MT7622 platforms need to enable LTSSM and ASPM from PCIe subsys */
> @@ -706,8 +705,7 @@ static int mtk_pcie_startup_port_v2(struct mtk_pcie_port *port)
>  		mtk_pcie_enable_msi(port);
>  
>  	/* Set AHB to PCIe translation windows */
> -	size = mem->end - mem->start;
> -	val = lower_32_bits(mem->start) | AHB2PCIE_SIZE(fls(size));
> +	val = lower_32_bits(mem->start) | AHB2PCIE_SIZE(fls(resource_size(mem)));

This is actually a fairly interesting change because it effectively
changes this:

  fls(mem->end - mem->start)

to this:

  fls(mem->end - mem->start + 1)

And mem->end is the last valid address, so it changes something like
this:

  fls(0xffff)         # == 15

to this:

  fls(0x10000)        # == 16

So while this *looks* like a trivial warning fix, it likely fixes an
important bug, and it's worth pointing out what that bug is in the
changelog.

>  	writel(val, port->base + PCIE_AHB_TRANS_BASE0_L);
>  
>  	val = upper_32_bits(mem->start);
> -- 
> 2.6.4
>