linux-kernel - Re: [PATCH 2/4] PCI: core: quirks: add mrrs_limit

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Message-ID: <CAL_JsqKV6iV1pbYNqFig5h5bH1cQ3pbdGc35F=sALNKdh2g4HA@mail.gmail.com>
Date:   Thu, 1 Jul 2021 11:07:34 -0600
From:   Rob Herring <robh@...nel.org>
To:     Artem Lapkin <email2tema@...il.com>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        Yue Wang <yue.wang@...ogic.com>,
        Kevin Hilman <khilman@...libre.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczynski <kw@...ux.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Christian Hewitt <christianshewitt@...il.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        PCI <linux-pci@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        art@...das.com, Nick Xie <nick@...das.com>, gouwa@...das.com
Subject: Re: [PATCH 2/4] PCI: core: quirks: add mrrs_limit_quirk

On Sat, Jun 19, 2021 at 12:40 AM Artem Lapkin <email2tema@...il.com> wrote:
>
> Prepare new MRRS limit quirk which can replace dublicated functionality

typo

> for some controllers from Loongson, Keystone, DesignWare
>
> Signed-off-by: Artem Lapkin <art@...das.com>
> ---
>  drivers/pci/quirks.c | 54 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 54 insertions(+)
>
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 653660e3b..73344ec71 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -5612,3 +5612,57 @@ static void apex_pci_fixup_class(struct pci_dev *pdev)
>  }
>  DECLARE_PCI_FIXUP_CLASS_HEADER(0x1ac1, 0x089a,
>                                PCI_CLASS_NOT_DEFINED, 8, apex_pci_fixup_class);
> +
> +/*
> + * Some Loongson PCIe ports have a h/w limitation of
> + * 256 bytes maximum read request size...
> + *
> + * Keystone PCI controller has a h/w limitation of
> + * 256 bytes maximum read request size.
> + *
> + * Amlogic DesignWare PCI controller on Khadas VIM3/VIM3L have some
> + * issue with HDMI scrambled picture and nvme devices
> + * at intensive writing...
> + */
> +static void mrrs_limit_quirk(struct pci_dev *dev)
> +{
> +       struct pci_bus *bus = dev->bus;
> +       struct pci_dev *bridge;
> +       int mrrs;
> +       int mrrs_limit = 256;
> +       static const struct pci_device_id bridge_devids[] = {
> +               { PCI_VDEVICE(LOONGSON, PCI_DEVICE_ID_LOONGSON_PCIE_PORT_0) },
> +               { PCI_VDEVICE(LOONGSON, PCI_DEVICE_ID_LOONGSON_PCIE_PORT_1) },
> +               { PCI_VDEVICE(LOONGSON, PCI_DEVICE_ID_LOONGSON_PCIE_PORT_2) },
> +               { PCI_DEVICE(PCI_VENDOR_ID_TI, PCI_DEVICE_ID_TI_RC_K2HK),
> +                .class = PCI_CLASS_BRIDGE_PCI << 8, .class_mask = ~0, },

Seems like checking the class is redundant given the VID and Device ID
seems to be pretty unique.

> +               { PCI_DEVICE(PCI_VENDOR_ID_TI, PCI_DEVICE_ID_TI_RC_K2E),
> +                .class = PCI_CLASS_BRIDGE_PCI << 8, .class_mask = ~0, },
> +               { PCI_DEVICE(PCI_VENDOR_ID_TI, PCI_DEVICE_ID_TI_RC_K2L),
> +                .class = PCI_CLASS_BRIDGE_PCI << 8, .class_mask = ~0, },
> +               { PCI_DEVICE(PCI_VENDOR_ID_TI, PCI_DEVICE_ID_TI_RC_K2G),
> +                .class = PCI_CLASS_BRIDGE_PCI << 8, .class_mask = ~0, },
> +               { PCI_DEVICE(PCI_VENDOR_ID_SYNOPSYS, PCI_DEVICE_ID_SYNOPSYS_HAPSUSB3) },

This is Amlogic I guess. But they are reusing the IP default values?
Any other vendor that does the same will get the same quirk applied?
These are write-able,
so perhaps the driver should set them to something Amlogic specific.

> +               { 0, },
> +       };
> +
> +       /* look for the matching bridge */
> +       while (!pci_is_root_bus(bus)) {
> +               bridge = bus->self;
> +               bus = bus->parent;
> +               /*
> +                * 256 bytes maximum read request size. They can't handle
> +                * anything larger than this. So force this limit on
> +                * any devices attached under these ports.
> +                */
> +               if (pci_match_id(bridge_devids, bridge)) {

I would invert this to save some indentation:

if (!pci_match_id(bridge_devids, bridge))
    continue;

> +                       mrrs = pcie_get_readrq(dev);
> +                       if (mrrs > mrrs_limit) {
> +                               pci_info(dev, "limiting MRRS %d to %d\n", mrrs, mrrs_limit);
> +                               pcie_set_readrq(dev, mrrs_limit);
> +                       }
> +                       break;
> +               }
> +       }
> +}
> +DECLARE_PCI_FIXUP_ENABLE(PCI_ANY_ID, PCI_ANY_ID, mrrs_limit_quirk);
> --
> 2.25.1
>