linux-kernel - Re: [PATCH] PCI: dwc: meson add quirk

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Date:   Fri, 18 Jun 2021 08:30:18 -0600
From:   Rob Herring <robh@...nel.org>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     Artem Lapkin <email2tema@...il.com>,
        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>,
        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] PCI: dwc: meson add quirk

On Fri, Jun 18, 2021 at 6:12 AM Martin Blumenstingl
<martin.blumenstingl@...glemail.com> wrote:
>
> Hi Artem,
>
> On Fri, Jun 18, 2021 at 8:38 AM Artem Lapkin <email2tema@...il.com> wrote:
> >
> > Device set same 256 bytes maximum read request size equal MAX_READ_REQ_SIZE
> > was find some issue with HDMI scrambled picture and nvme devices
> > at intensive writing...
> >
> > [    4.798971] nvme 0000:01:00.0: fix MRRS from 512 to 256
> >
> > This quirk setup same MRRS if we try solve this problem with
> > pci=pcie_bus_perf kernel command line param
> thank you for investigating this issue and for providing a fix!
>
> [...]
> > +static void meson_pcie_quirk(struct pci_dev *dev)
> > +{
> > +       int mrrs;
> > +
> > +       /* no need quirk */
> > +       if (pcie_bus_config != PCIE_BUS_DEFAULT)
> > +               return;
> > +
> > +       /* no need for root bus */
> > +       if (pci_is_root_bus(dev->bus))
> > +               return;
> > +
> > +       mrrs = pcie_get_readrq(dev);
> > +
> > +       /*
> > +        * set same 256 bytes maximum read request size equal MAX_READ_REQ_SIZE
> > +        * was find some issue with HDMI scrambled picture and nvme devices
> > +        * at intensive writing...
> > +        */
> > +
> > +       if (mrrs != MAX_READ_REQ_SIZE) {
> > +               dev_info(&dev->dev, "fix MRRS from %d to %d\n", mrrs, MAX_READ_REQ_SIZE);
> > +               pcie_set_readrq(dev, MAX_READ_REQ_SIZE);
> > +       }
> > +}
> > +DECLARE_PCI_FIXUP_ENABLE(PCI_ANY_ID, PCI_ANY_ID, meson_pcie_quirk);

Isn't this going to run for everyone if meson driver happens to be enabled?

> it seems that other PCIe controllers need something similar. in
> particular I found pci-keystone [0] and pci-loongson [1]
> while comparing your code with the two existing implementations two
> things came to my mind:
> 1. your implementation slightly differs from the two existing ones as
> it's not walking through the parent PCI busses (I think this would be
> relevant if there's another bridge between the host bridge and the
> actual device)
> 2. (this is a question towards the PCI maintainers) does it make sense
> to have this MRRS quirk re-usable somewhere?

Yes. Ideally, the max size could just be data in the bus or bridge
struct and perhaps some flags too, then the core can handle
everything.

Rob