From: Rob Herring <robh@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Jisheng Zhang <Jisheng.Zhang@synaptics.com>,
Kishon Vijay Abraham I <kishon@ti.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Jingoo Han <jingoohan1@gmail.com>,
Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
Thierry Reding <treding@nvidia.com>,
Vidya Sagar <vidyas@nvidia.com>, PCI <linux-pci@vger.kernel.org>,
linux-omap <linux-omap@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] PCI: dwc: Move allocate and map page for msi out of dw_pcie_msi_init()
Date: Thu, 24 Sep 2020 07:28:25 -0600 [thread overview]
Message-ID: <CAL_JsqLkQ_NqrDDJZkm5ef-mf4_Vh0sW1DqQjitz-GzGBNbWhA@mail.gmail.com> (raw)
In-Reply-To: <CAMj1kXEyQGEu7=-kbDuTDW9_xXkmns1HM2dQMrLn=XL9W88vJw@mail.gmail.com>
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/
next prev parent reply other threads:[~2020-09-24 13:28 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 6:26 [PATCH] PCI: dwc: Move allocate and map page for msi out of dw_pcie_msi_init() Jisheng Zhang
2020-09-23 16:41 ` Rob Herring
2020-09-24 7:02 ` Jisheng Zhang
2020-09-24 11:00 ` Ard Biesheuvel
2020-09-24 13:28 ` Rob Herring [this message]
2020-09-24 13:45 ` Ard Biesheuvel
2020-09-24 14:32 ` Ard Biesheuvel
2020-09-24 15:09 ` Rob Herring
2020-09-25 8:56 ` Jisheng Zhang
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