Re: [PATCH] PCI: dwc: Move allocate and map page for msi out of dw_pcie_msi_init()
From: Ard Biesheuvel <ardb@kernel.org>
Date: 2020-09-24 14:33:13
Also in:
linux-omap, linux-pci, lkml
On Thu, 24 Sep 2020 at 15:45, Ard Biesheuvel [off-list ref] wrote:
On Thu, 24 Sep 2020 at 15:28, Rob Herring [off-list ref] wrote:quoted
On Thu, Sep 24, 2020 at 5:00 AM Ard Biesheuvel [off-list ref] wrote:quoted
On Wed, 23 Sep 2020 at 08:28, Jisheng Zhang [off-list ref] wrote:quoted
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 <redacted>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].quoted
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.PCIE_MSI_ADDR_LO itself could collide with an actual DRAM address if any translation is applied on inbound transactions. Using an actual DRAM address avoids that.
... although the MSI doorbell register on the GIC, for instance, needs to be DMA addressable as well, of course. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel