Messages in this thread | | | From | Rob Herring <> | Date | Thu, 24 Sep 2020 07:28:25 -0600 | Subject | Re: [PATCH] PCI: dwc: Move allocate and map page for msi out of dw_pcie_msi_init() |
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On Thu, Sep 24, 2020 at 5:00 AM Ard Biesheuvel <ardb@kernel.org> wrote: > > On Wed, 23 Sep 2020 at 08:28, Jisheng Zhang <Jisheng.Zhang@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@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 > PCIE_MSI_INTR0_STATUS ?
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 do.
Rob
[1] https://lore.kernel.org/linux-pci/20200923231846.GA1499246@bogus/
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