Re: [PATCH] PCI: brcmstb: Assign pcie->gen from pcie_get_link_speed()

[Florian Fainelli <florian.fainelli@broadcom.com>]

On 5/5/26 09:01, Bjorn Helgaas wrote:
> On Mon, May 04, 2026 at 04:46:03PM -0700, Florian Fainelli wrote:
>> On 5/4/26 10:26, Hans Zhang wrote:
>>> On 5/5/26 00:58, Florian Fainelli wrote:
>>>> On 5/2/26 04:40, Bjorn Helgaas wrote:
>>>>> On Fri, May 01, 2026 at 01:24:38PM -0700, Florian Fainelli wrote:
>>>>>> After commit 03f920936977 ("PCI: controller: Validate max-link-speed"),
>>>>>> pcie->gen stopped being assigned and as a result the established PCIe
>>>>>> link would stop supporting Gen3 speeds on 2712 since pcie->gen is used
>>>>>> to populate LnkCntl2 and LnkCap in brcm_pcie_set_gen().
>>>>>>
>>>>>> Link: https://github.com/raspberrypi/linux/issues/7343
>>>>>> Reported-by: Dom Cobley <popcornmix@gmail.com>
>>>>>> Reported-by: Phil Elwell <phil@raspberrypi.com>
>>>>>> Fixes: 03f920936977 ("PCI: controller: Validate max-link-speed")
>>>>>> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
>>>>>> ---
>>>>>>    drivers/pci/controller/pcie-brcmstb.c | 3 +--
>>>>>>    1 file changed, 1 insertion(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/pci/controller/pcie-brcmstb.c
>>>>>> b/drivers/pci/ controller/pcie-brcmstb.c
>>>>>> index 714bcab97b60..6138fc4bc064 100644
>>>>>> --- a/drivers/pci/controller/pcie-brcmstb.c
>>>>>> +++ b/drivers/pci/controller/pcie-brcmstb.c
>>>>>> @@ -2072,8 +2072,7 @@ static int brcm_pcie_probe(struct
>>>>>> platform_device *pdev)
>>>>>>            return PTR_ERR(pcie->clk);
>>>>>>        ret = of_pci_get_max_link_speed(np);
>>>>>> -    if (pcie_get_link_speed(ret) == PCI_SPEED_UNKNOWN)
>>>>>> -        pcie->gen = 0;
>>>>>> +    pcie->gen = pcie_get_link_speed(ret);
>>>>>
>>>>> Take a look at https://sashiko.dev/#/
>>>>> patchset/20260501202438.376033-1-
>>>>> florian.fainelli%40broadcom.com
>>>>>
>>>>> The notes at https://github.com/raspberrypi/linux/issues/7343 assumed
>>>>> PCI_SPEED_UNKNOWN was 0, but in fact it is 0xff, which means you might
>>>>> want the more defensive patch instead.
>>>>>
>>>>> I'll be happy to replace what's on pci/for-linus if so.
>>>>
>>>> I am starting to think a revert is the simplest path forward, it's
>>>> not clear what pcie_get_link_speed() brings to the table honestly.
>>>
>>> The pcie_get_link_speed function is designed to prevent other Root Port
>>> drivers from accessing the array pcie_link_speed out of bounds.
>>
>> Yes, so that's useful in the first hunk of your commit where we were
>> printing the link speed without checking that the 'max-link-speed' would be
>> bounds check, however it is not really useful for assigning to pcie->gen in
>> our case, so I would prefer the second option:
>>
>>            ret = of_pci_get_max_link_speed(np);
>>   -       if (pcie_get_link_speed(ret) == PCI_SPEED_UNKNOWN)
>>   -               pcie->gen = 0;
>>   +       pcie->gen = (ret < 0) ? 0 : ret;
> 
> The point of this validation is to make sure we don't program the
> brcmstb hardware with something it doesn't support.
> 
> of_pci_get_max_link_speed() only returns an error (ret < 0) if DT
> didn't contain a 'max-link-speed' property.  That doesn't tell us
> anything about what brcmstb devices support.
> 
> I think this test should be something like what advk_pcie_probe() or
> rockchip_pcie_parse_dt() do.  If of_pci_get_max_link_speed() fails or
> returns something not supported by the hardware, they default to the
> fastest speed known to be supported.

Doing that could be challenging because it varies on a per-controller 
instance on some chips like 2712, this would also be a behavioral 
difference compared to today where the driver resorts to HW-defaults if 
the property is not specified.

There is also another aspect we have ignored which is that don't 
currently support anything beyond Gen3 at this point, but this is not 
enforced. Let me cook another patch.
-- 
Florian