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

Hans Zhang
2025-04-18T17:22:38Z

On 2025/4/18 22:55, Niklas Cassel wrote:
>
>
> On 18 April 2025 14:33:08 CEST, Hans Zhang <18255117159@163.com> 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