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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Thu, 24 Sep 2020 13:00:26 +0200
Message-ID: <CAMj1kXEyQGEu7=-kbDuTDW9_xXkmns1HM2dQMrLn=XL9W88vJw@mail.gmail.com>
Subject: Re: [PATCH] PCI: dwc: Move allocate and map page for msi out of dw_pcie_msi_init()
To:     Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Cc:     Kishon Vijay Abraham I <kishon@ti.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Rob Herring <robh@kernel.org>,
        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>, linux-pci@vger.kernel.org,
        linux-omap@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
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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 ?

Couldn't you just map the zero page instead?


> ---
>  drivers/pci/controller/dwc/pci-dra7xx.c       | 18 ++++++++++++-
>  .../pci/controller/dwc/pcie-designware-host.c | 27 +++++++++----------
>  2 files changed, 30 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pci-dra7xx.c b/drivers/pci/controller/dwc/pci-dra7xx.c
> index dc387724cf08..4301cf844a4c 100644
> --- a/drivers/pci/controller/dwc/pci-dra7xx.c
> +++ b/drivers/pci/controller/dwc/pci-dra7xx.c
> @@ -490,7 +490,9 @@ static struct irq_chip dra7xx_pci_msi_bottom_irq_chip = {
>  static int dra7xx_pcie_msi_host_init(struct pcie_port *pp)
>  {
>         struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +       struct device *dev = pci->dev;
>         u32 ctrl, num_ctrls;
> +       int ret;
>
>         pp->msi_irq_chip = &dra7xx_pci_msi_bottom_irq_chip;
>
> @@ -506,7 +508,21 @@ static int dra7xx_pcie_msi_host_init(struct pcie_port *pp)
>                                     ~0);
>         }
>
> -       return dw_pcie_allocate_domains(pp);
> +       ret = dw_pcie_allocate_domains(pp);
> +       if (ret)
> +               return ret;
> +
> +       pp->msi_page = alloc_page(GFP_KERNEL);
> +       pp->msi_data = dma_map_page(dev, pp->msi_page, 0, PAGE_SIZE,
> +                                   DMA_FROM_DEVICE);
> +       ret = dma_mapping_error(dev, pp->msi_data);
> +       if (ret) {
> +               dev_err(dev, "Failed to map MSI data\n");
> +               __free_page(pp->msi_page);
> +               pp->msi_page = NULL;
> +               dw_pcie_free_msi(pp);
> +       }
> +       return ret;
>  }
>
>  static const struct dw_pcie_host_ops dra7xx_pcie_host_ops = {
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 9dafecba347f..c23ba64f64fe 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -294,20 +294,7 @@ void dw_pcie_free_msi(struct pcie_port *pp)
>
>  void dw_pcie_msi_init(struct pcie_port *pp)
>  {
> -       struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> -       struct device *dev = pci->dev;
> -       u64 msi_target;
> -
> -       pp->msi_page = alloc_page(GFP_KERNEL);
> -       pp->msi_data = dma_map_page(dev, pp->msi_page, 0, PAGE_SIZE,
> -                                   DMA_FROM_DEVICE);
> -       if (dma_mapping_error(dev, pp->msi_data)) {
> -               dev_err(dev, "Failed to map MSI data\n");
> -               __free_page(pp->msi_page);
> -               pp->msi_page = NULL;
> -               return;
> -       }
> -       msi_target = (u64)pp->msi_data;
> +       u64 msi_target = (u64)pp->msi_data;
>
>         /* Program the msi_data */
>         dw_pcie_wr_own_conf(pp, PCIE_MSI_ADDR_LO, 4,
> @@ -440,6 +427,18 @@ int dw_pcie_host_init(struct pcie_port *pp)
>                                 irq_set_chained_handler_and_data(pp->msi_irq,
>                                                             dw_chained_msi_isr,
>                                                             pp);
> +
> +                       pp->msi_page = alloc_page(GFP_KERNEL);
> +                       pp->msi_data = dma_map_page(pci->dev, pp->msi_page,
> +                                                   0, PAGE_SIZE,
> +                                                   DMA_FROM_DEVICE);
> +                       ret = dma_mapping_error(pci->dev, pp->msi_data);
> +                       if (ret) {
> +                               dev_err(pci->dev, "Failed to map MSI data\n");
> +                               __free_page(pp->msi_page);
> +                               pp->msi_page = NULL;
> +                               goto err_free_msi;
> +                       }
>                 } else {
>                         ret = pp->ops->msi_host_init(pp);
>                         if (ret < 0)
> --
> 2.28.0
>
>
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