linux-kernel - Re: [PATCH v3 2/2] PCI: dwc: Use an address in the driver data for MSI address

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Message-ID: <20200927172238.548912fe@xhacker.debian>
Date:   Sun, 27 Sep 2020 17:23:23 +0800
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        PCI <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Niklas Cassel <nks@...wful.org>
Subject: Re: [PATCH v3 2/2] PCI: dwc: Use an address in the driver data for
 MSI address

On Fri, 25 Sep 2020 09:33:54 -0600 Rob Herring wrote:


> 
> +Niklas
> 
> On Fri, Sep 25, 2020 at 2:39 AM Jisheng Zhang
> <Jisheng.Zhang@...aptics.com> wrote:
> >
> > There's no need to allocate a page for the MSI address, we could use
> > an address in the driver data.
> >
> > One side effect of this patch is fixing the MSI page leakage during
> > suspend/resume. Take the pcie-tegra194.c for example, it calls
> > dw_pcie_msi_init() in resume path, thus the previous MSI page is
> > leaked.
> >
> > Fixes: 56e15a238d92 ("PCI: tegra: Add Tegra194 PCIe support")
> > Suggested-by: Rob Herring <robh@...nel.org>
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
> > ---
> >  .../pci/controller/dwc/pcie-designware-host.c | 22 ++-----------------
> >  drivers/pci/controller/dwc/pcie-designware.h  |  1 -
> >  2 files changed, 2 insertions(+), 21 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index f08f4d97f321..bf25d783b5c5 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -126,9 +126,7 @@ static void dw_pci_setup_msi_msg(struct irq_data *d, struct msi_msg *msg)
> >  {
> >         struct pcie_port *pp = irq_data_get_irq_chip_data(d);
> >         struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> > -       u64 msi_target;
> > -
> > -       msi_target = (u64)pp->msi_data;
> > +       u64 msi_target = virt_to_phys(&pp->msi_data);
> >
> >         msg->address_lo = lower_32_bits(msi_target);
> >         msg->address_hi = upper_32_bits(msi_target);
> > @@ -287,27 +285,11 @@ void dw_pcie_free_msi(struct pcie_port *pp)
> >
> >         irq_domain_remove(pp->msi_domain);
> >         irq_domain_remove(pp->irq_domain);
> > -
> > -       if (pp->msi_page)
> > -               __free_page(pp->msi_page);
> >  }
> >
> >  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);

I checked commit 111111a72e677ff13 ("PCI: dwc: Use the DMA-API to get the MSI
address") again, I think we need dma_map_single() here, either due to 

The phy address is different with dma address on some systems

or

All memory isn't accessible from PCIe RC on some systems

dma_map_single() could work on all systems. But this leaves a problem: how
to avoid the map again during resume? A simple solution would be:

move the dma_map_single out of dw_pcie_msi_init() as V1 does, sure,
pci-dra7xx.c needs to call dma_map_single() itself.

Is this acceptable?

Thanks

> > -       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 = virt_to_phys(&pp->msi_data);
> >
> >         /* Program the msi_data */
> >         dw_pcie_wr_own_conf(pp, PCIE_MSI_ADDR_LO, 4,