Re: [PATCH v2 1/1] PCI: mediatek: Correct type for virt_to_phys()

From: Bjorn Helgaas <helgaas@kernel.org>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: linux-pci@vger.kernel.org, linux-mediatek@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	"Ryder Lee" <ryder.lee@mediatek.com>,
	"Jianjun Wang" <jianjun.wang@mediatek.com>,
	"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Rob Herring" <robh@kernel.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"AngeloGioacchino Del Regno"
	<angelogioacchino.delregno@collabora.com>,
	"Huacai Chen" <chenhuacai@kernel.org>,
	"kernel test robot" <lkp@intel.com>
Subject: Re: [PATCH v2 1/1] PCI: mediatek: Correct type for virt_to_phys()
Date: Thu, 14 Sep 2023 15:31:46 -0500	[thread overview]
Message-ID: <20230914203146.GA77870@bhelgaas> (raw)
In-Reply-To: <20230914192324.672997-1-andriy.shevchenko@linux.intel.com>

On Thu, Sep 14, 2023 at 10:23:24PM +0300, Andy Shevchenko wrote:
> virt_to_phys() takes a regular pointer, while driver supplies __iomem
> annotated one. Force type to void to make sparse happy, otherwise
> 
>    pcie-mediatek.c:400:40: sparse:     expected void volatile *address
>    pcie-mediatek.c:400:40: sparse:     got void [noderef] __iomem *
> 
>    pcie-mediatek.c:523:44: sparse:     expected void volatile *address
>    pcie-mediatek.c:523:44: sparse:     got void [noderef] __iomem *
> 
> Reported-by: Huacai Chen <chenhuacai@kernel.org>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202309072237.9zxMv4MZ-lkp@intel.com/
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.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..5e795afd1cee 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 void *)port->base + PCIE_MSI_VECTOR);

Lots of these drivers use either virt_to_phys() or
platform_get_resource_byname() to get a physical address that they
then use as the MSI target.

But I don't think that's quite right -- the MSI is a DMA transaction
on PCI, and in general there's no guarantee that bus addresses are
identical to CPU physical addresses, so shouldn't we use a dma_addr_t
obtained from the DMA API?

dw_pcie_msi_host_init() has a complicated version of this that uses
dmam_alloc_coherent().

>  	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 void *)port->base + PCIE_MSI_VECTOR);
>  	val = lower_32_bits(msg_addr);
>  	writel(val, port->base + PCIE_IMSI_ADDR);
>  
> -- 
> 2.40.0.1.gaa8946217a0b
> 
> 
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