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

From: Honghui Zhang <honghui.zhang@mediatek.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: youlin.pei@mediatek.com, lorenzo.pieralisi@arm.com,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
	jianjun.wang@mediatek.com, ryder.lee@mediatek.com,
	linux-mediatek@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] PCI: Mediatek: Use resource_size function on resource object
Date: Thu, 31 Jan 2019 11:03:53 +0800	[thread overview]
Message-ID: <1548903833.22019.26.camel@mhfsdcap03> (raw)
In-Reply-To: <20190130154950.GD229773@google.com>

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
> > 

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