linux-kernel - Re: [PATCH v2 1/1] PCI: mediatek: Correct type for virt_to

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Message-ID: <ZQWGd/RyKaUBRhUY@smile.fi.intel.com>
Date:   Sat, 16 Sep 2023 13:41:59 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-pci@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Ryder Lee <ryder.lee@...iatek.com>,
        Jianjun Wang <jianjun.wang@...iatek.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2 1/1] PCI: mediatek: Correct type for virt_to_phys()

On Thu, Sep 14, 2023 at 03:31:46PM -0500, Bjorn Helgaas wrote:
> On Thu, Sep 14, 2023 at 10:23:24PM +0300, Andy Shevchenko wrote:

...

> > -	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().

Fair enough. I leave it to you then to get it fixed properly.
Consider this as just a heads up for the old report.

-- 
With Best Regards,
Andy Shevchenko