Re: [PATCH] PCI: dwc: meson add quirk

On Fri, Jun 18, 2021 at 6:12 AM Martin Blumenstingl
[off-list ref] wrote:

Hi Artem,

On Fri, Jun 18, 2021 at 8:38 AM Artem Lapkin [off-list ref] wrote:

quoted

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!

[...]

quoted

+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

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