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Date:   Fri, 25 Sep 2020 16:56:44 +0800
From:   Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To:     Rob Herring <robh@kernel.org>,
        Niklas Cassel <niklas.cassel@axis.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>,
        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()
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On Thu, 24 Sep 2020 07:28:25 -0600
Rob Herring <robh@kernel.org> wrote:

> CAUTION: Email originated externally, do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> 
> 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.
> 

Thank Ard and Rob. I have sent out V3 (https://lkml.org/lkml/2020/9/25/272)
which uses an address in the driver data for MSI address.


Hi Niklas,

can you please try v3 to see whether it solves your problem as well?

Thanks