[PATCH] PCI: dwc: Move allocate and map page for msi out of dw_pcie_msi_init()

Rob Herring robh at kernel.org
Thu Sep 24 09:28:25 EDT 2020

On Thu, Sep 24, 2020 at 5:00 AM Ard Biesheuvel <ardb at kernel.org> wrote:
> On Wed, 23 Sep 2020 at 08:28, Jisheng Zhang <Jisheng.Zhang at synaptics.com> wrote:
> >
> > Currently, dw_pcie_msi_init() allocates and maps page for msi, then
> > program the PCIE_MSI_ADDR_LO and PCIE_MSI_ADDR_HI. The Root Complex
> > may lose power during suspend-to-RAM, so when we resume, we want to
> > redo the latter but not the former. If designware based driver (for
> > example, pcie-tegra194.c) calls dw_pcie_msi_init() in resume path, the
> > previous msi page will be leaked.
> >
> > Move the allocate and map msi page from dw_pcie_msi_init() to
> > dw_pcie_host_init() to fix this problem.
> >
> > Fixes: 56e15a238d92 ("PCI: tegra: Add Tegra194 PCIe support")
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang at synaptics.com>
> Why do you allocate a page for this in the first place? Isn't
> PCIE_MSI_ADDR_HI:PCIE_MSI_ADDR_LO simply a magic DMA address that
> never gets forwarded across to the CPU side of the host bridge, and
> triggers a SPI instead, which gets handled by reading

My question too after digging into this some more. I've asked the
question on the thread that further complicated all this changing from
virt_to_phys() to dma_map_page()[1].

> Couldn't you just map the zero page instead?

Why a page even? You could use PCIE_MSI_ADDR_LO address itself even.
Or just an address in the driver data which is what some other drivers


[1] https://lore.kernel.org/linux-pci/20200923231846.GA1499246@bogus/

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