Re: [PATCH] PCI: mediatek: Fix sparse warning caused to virt_to_phys() prototype change

From: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: ryder.lee@mediatek.com, jianjun.wang@mediatek.com,
	lpieralisi@kernel.org, kw@linux.com, robh@kernel.org,
	bhelgaas@google.com, matthias.bgg@gmail.com,
	angelogioacchino.delregno@collabora.com,
	linux-pci@vger.kernel.org, linux-mediatek@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, skinsburskii@gmail.com
Subject: Re: [PATCH] PCI: mediatek: Fix sparse warning caused to virt_to_phys() prototype change
Date: Tue, 21 Nov 2023 14:05:56 -0800	[thread overview]
Message-ID: <20231121220556.GA21969@skinsburskii.> (raw)
In-Reply-To: <20231121213755.GA258354@bhelgaas>

On Tue, Nov 21, 2023 at 03:37:55PM -0600, Bjorn Helgaas wrote:
> On Mon, Nov 20, 2023 at 03:40:33PM -0800, Stanislav Kinsburskii wrote:
> > Explicitly cast __iomem pointer to const void* with __force to fix the
> > following warning:
> > 
> >   warning: incorrect type in argument 1 (different address spaces)
> >      expected void const volatile *address
> >      got void [noderef] __iomem *
> 
> I have two questions about this:
> 
>   1) There's no other use of __force in drivers/pci, so I don't know
>   what's special about pcie-mediatek.c.  There should be a way to fix
>   the types so it's not needed.
> 

__force suppreses the following sparse warning:

    warning: cast removes address space '__iomem' of expression

>   2) virt_to_phys() is not quite right to begin with because what we
>   want is a *bus* address, not the CPU physical address we get from
>   virt_to_phys().  Obviously the current platforms that use this must
>   not apply any offset between bus and CPU physical addresses, but
>   it's not something we should rely on.
> 
>   There are only three drivers (pci-aardvark.c, pcie-xilinx.c, and
>   this one) that use virt_to_phys(), and they're all slightly wrong
>   here.
> 
> The *_compose_msi_msg() methods could use a little more consistency
> across the board.
> 

Could you elaborate on what do you suggest?
Should virt_to_phys() be simply removed?

> > Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> > ---
> >  drivers/pci/controller/pcie-mediatek.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
> > index 66a8f73296fc..27f0f79810a1 100644
> > --- a/drivers/pci/controller/pcie-mediatek.c
> > +++ b/drivers/pci/controller/pcie-mediatek.c
> > @@ -397,7 +397,7 @@ static void mtk_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
> >  	phys_addr_t addr;
> >  
> >  	/* MT2712/MT7622 only support 32-bit MSI addresses */
> > -	addr = virt_to_phys(port->base + PCIE_MSI_VECTOR);
> > +	addr = virt_to_phys((__force const void *)port->base + PCIE_MSI_VECTOR);
> >  	msg->address_hi = 0;
> >  	msg->address_lo = lower_32_bits(addr);
> >  
> > @@ -520,7 +520,7 @@ static void mtk_pcie_enable_msi(struct mtk_pcie_port *port)
> >  	u32 val;
> >  	phys_addr_t msg_addr;
> >  
> > -	msg_addr = virt_to_phys(port->base + PCIE_MSI_VECTOR);
> > +	msg_addr = virt_to_phys((__force const void *)port->base + PCIE_MSI_VECTOR);
> >  	val = lower_32_bits(msg_addr);
> >  	writel(val, port->base + PCIE_IMSI_ADDR);
> >  
> > 
> > 
> > 

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