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

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Message-ID: <20250418162118.GA157636@bhelgaas>
Date: Fri, 18 Apr 2025 11:21:18 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Niklas Cassel <cassel@...nel.org>
Cc: Hans Zhang <18255117159@....com>, Shawn Lin <shawn.lin@...k-chips.com>,
	lpieralisi@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
	heiko@...ech.de, manivannan.sadhasivam@...aro.org, robh@...nel.org,
	jingoohan1@...il.com, thomas.richard@...tlin.com,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH] PCI: dw-rockchip: Configure max payload size on host init

On Fri, Apr 18, 2025 at 04:55:13PM +0200, Niklas Cassel wrote:
> On 18 April 2025 14:33:08 CEST, Hans Zhang <18255117159@....com> wrote:
> >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?
> 
> 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);
> +
>          /*
>           * 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.

Thanks, Niklas, this seems like a reasonable place to start.
Hopefully we can drop the controller-specific quirks since there's
nothing controller-specific about them.

Bjorn