Re: [PATCH v3 REPOST] PCIe: limit Max Read Request Size on i.MX to 512 bytes

[Art Nikpal]

On Fri, Oct 8, 2021 at 3:19 PM Richard Zhu <hongxing.zhu@xxxxxxx> wrote:
>
> > -----Original Message-----
> > From: Krzysztof Hałasa <khalasa@xxxxxxx>
> > Sent: Wednesday, October 6, 2021 2:17 PM
> > To: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > Cc: linux-pci@xxxxxxxxxxxxxxx; Artem Lapkin <email2tema@xxxxxxxxx>; Neil
> > Armstrong <narmstrong@xxxxxxxxxxxx>; Huacai Chen
> > <chenhuacai@xxxxxxxxx>; Rob Herring <robh@xxxxxxxxxx>; Lorenzo Pieralisi
> > <lorenzo.pieralisi@xxxxxxx>; Krzysztof Wilczyński <kw@xxxxxxxxx>; Richard
> > Zhu <hongxing.zhu@xxxxxxx>; Lucas Stach <l.stach@xxxxxxxxxxxxxx>;
> > linux-kernel@xxxxxxxxxxxxxxx
> > Subject: [PATCH v3 REPOST] PCIe: limit Max Read Request Size on i.MX to 512
> > bytes
> >
> > DWC PCIe controller imposes limits on the Read Request Size that it can
> > handle. For i.MX6 family it's fixed at 512 bytes by default.
> >
> > If a memory read larger than the limit is requested, the CPU responds with
> > Completer Abort (CA) (on i.MX6 Unsupported Request (UR) is returned
> > instead due to a design error).
> >
> > The i.MX6 documentation states that the limit can be changed by writing to
> > the PCIE_PL_MRCCR0 register, however there is a fixed (and
> > undocumented) maximum (CX_REMOTE_RD_REQ_SIZE constant). Tests
> > indicate that values larger than 512 bytes don't work, though.
> >
> > This patch makes the RTL8111 work on i.MX6.
> >
> > Signed-off-by: Krzysztof Hałasa <khalasa@xxxxxxx>
> [Richard Zhu] I'm fine with this patch. Acked-by: Richard Zhu <hongxing.zhu@xxxxxxx>. Thanks.

Same will be fine for us

>
> Best Regards
> Richard Zhu
>
> > ---
> > While ATM needed only on ARM, this version is compiled in on all archs.
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index 80fc98acf097..225380e75fff 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -1148,6 +1148,7 @@ static int imx6_pcie_probe(struct platform_device
> > *pdev)
> >               imx6_pcie->vph = NULL;
> >       }
> >
> > +     max_pcie_mrrs = 512;
> >       platform_set_drvdata(pdev, imx6_pcie);
> >
> >       ret = imx6_pcie_attach_pd(dev);
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index
> > aacf575c15cf..abeb48a64ee3 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -112,6 +112,8 @@ enum pcie_bus_config_types pcie_bus_config =
> > PCIE_BUS_PEER2PEER;  enum pcie_bus_config_types pcie_bus_config =
> > PCIE_BUS_DEFAULT;  #endif
> >
> > +u16 max_pcie_mrrs = 4096; // no limit
> > +
> >  /*
> >   * The default CLS is used if arch didn't set CLS explicitly and not
> >   * all pci devices agree on the same value.  Arch can override either @@
> > -5816,6 +5818,9 @@ int pcie_set_readrq(struct pci_dev *dev, int rq)
> >                       rq = mps;
> >       }
> >
> > +     if (rq > max_pcie_mrrs)
> > +             rq = max_pcie_mrrs;
> > +
> >       v = (ffs(rq) - 8) << 12;
> >
> >       ret = pcie_capability_clear_and_set_word(dev, PCI_EXP_DEVCTL, diff
> > --git a/include/linux/pci.h b/include/linux/pci.h index
> > 06ff1186c1ef..2b95a8204819 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -996,6 +996,7 @@ enum pcie_bus_config_types {  };
> >
> >  extern enum pcie_bus_config_types pcie_bus_config;
> > +extern u16 max_pcie_mrrs;
> >
> >  extern struct bus_type pci_bus_type;
> >
> >
> > --
> > Krzysztof "Chris" Hałasa
> >
> > Sieć Badawcza Łukasiewicz
> > Przemysłowy Instytut Automatyki i Pomiarów PIAP Al. Jerozolimskie 202,
> > 02-486 Warszawa