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

Honghui Zhang
2019-01-31T03:03:53Z

On Wed, 2019-01-30 at 09:49 -0600, Bjorn Helgaas wrote:
> On Wed, Jan 02, 2019 at 02:03:53PM +0800, honghui.zhang@mediatek.com wrote:
> > From: Honghui Zhang <honghui.zhang@mediatek.com>
> >
> > 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@mediatek.com>
> > ---
> > 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);

This size will set the MMIO size, which means that the RC will translate
the MMIO access from mem->start to mem->end.
The real MMIO size is specified in devicetree, which is 0x1000_0000 for
both mt2712 and mt7622.

This change make the size from fls(0x1000_0000) to fls(0x1000_0001), not
really change the values.

I will update the commit message and add the information mentioned
above.

Thanks for your kindly review.

> > --
> > 2.6.4
> >