Re: [PATCH] PCI: dw-rockchip: Configure max payload size on host init

[Hans Zhang]

On 2025/4/18 22:55, Niklas Cassel wrote:
> On 18 April 2025 14:33:08 CEST, Hans Zhang <18255117159@xxxxxxx> wrote:
> > Dear Bjorn,
> >
> > Thanks your for reply. Niklas and I attempted to modify the relevant logic in drivers/pci/probe.c and found that there was a lot of code judging the global variable pcie_bus_config. At present, there is no good method. I will keep trying.
> >
> > I wonder if you have any good suggestions? It seems that the code logic regarding pcie_bus_config is a little complicated and cannot be modified for the time being?
>
>
> Hans,
>
> If:
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 364fa2a514f8..2e1c92fdd577 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2983,6 +2983,13 @@ void pcie_bus_configure_settings(struct pci_bus *bus)
>           if (!pci_is_pcie(bus->self))
>                   return;
>    +       /*
> +        * Start off with DevCtl.MPS == DevCap.MPS, unless PCIE_BUS_TUNE_OFF.
> +        * This might get overriden by a MPS strategy below.
> +        */
> +       if (pcie_bus_config != PCIE_BUS_TUNE_OFF)
> +               smpss = pcie_get_mps(bus->self);
> +

Dear Niklas,

Thank you very much for your reply and thoughts.

pcie_get_mps: Returns maximum payload size in bytes

I guess you want to obtain the DevCap MPS. But the purpose of the smpss 
variable is to save the DevCtl MPS.

>           /*
>            * FIXME - Peer to peer DMA is possible, though the endpoint would need
>            * to be aware of the MPS of the destination.  To work around this,
>
>
>
> does not work, can't you modify the code slightly so that it works?
>
> I haven't tried myself, but considering that it works when walking the bus, it seems that it should be possible to get something working.


After making the following modifications, my test shows that it is 
normal. If the consideration is not comprehensive. Could Bjorn and 
Niklas please review my revisions?

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 364fa2a514f8..5b54f1b0a91d 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2951,8 +2951,7 @@ static int pcie_bus_configure_set(struct pci_dev 
*dev, void *data)
        if (!pci_is_pcie(dev))
                return 0;

-       if (pcie_bus_config == PCIE_BUS_TUNE_OFF ||
-           pcie_bus_config == PCIE_BUS_DEFAULT)
+       if (pcie_bus_config == PCIE_BUS_TUNE_OFF)
                return 0;

        mps = 128 << *(u8 *)data;
@@ -2991,7 +2990,8 @@ void pcie_bus_configure_settings(struct pci_bus *bus)
        if (pcie_bus_config == PCIE_BUS_PEER2PEER)
                smpss = 0;

-       if (pcie_bus_config == PCIE_BUS_SAFE) {
+       if ((pcie_bus_config == PCIE_BUS_SAFE) ||
+           (pcie_bus_config != PCIE_BUS_TUNE_OFF)) {
                smpss = bus->self->pcie_mpss;

                pcie_find_smpss(bus->self, &smpss);


Best regards,
Hans