Re: [PATCH net 1/2] net: stmmac: Limit FIFO size by hardware feature value

[Kunihiko Hayashi <hayashi.kunihiko@socionext.com>]

Hi Andrew,

On 2025/01/21 1:29, Andrew Lunn wrote:
> On Mon, Jan 20, 2025 at 02:20:23PM +0900, Kunihiko Hayashi wrote:
>> Hi Andrew,
>>
>> On 2025/01/17 5:16, Andrew Lunn wrote:
>>> On Thu, Jan 16, 2025 at 11:08:52AM +0900, Kunihiko Hayashi wrote:
>>>> Tx/Rx FIFO size is specified by the parameter "{tx,rx}-fifo-depth"
> from
>>>> the platform layer.
>>>>
>>>> However, these values are constrained by upper limits determined by
> the
>>>> capabilities of each hardware feature. There is a risk that the
> upper
>>>> bits will be truncated due to the calculation, so it's appropriate
> to
>>>> limit them to the upper limit values.
>>>
>>> Are these values hard coded in the platform layer? Or can they come
>>> from userspace?
>>
>> My explanation is insufficient and misleading.
>> "From the platform layer" means the common layer of stmmac described in
>> "stmmac_platform.c".
>>
>>> If they are hard coded, we should also fix them. So maybe add a
>>> netdev_warn(), and encourage the platform maintainers to fix their
>>> platform. If they are coming from userspace, we should consider
>>> failing the ethtool call with an -EINVAL, and maybe an extack with the
>>> valid range?
>>
>> These values are derived from the devicetree and stored in the stmmac
>> private structure. They are hardware-specific values, so I think this
>> fix is sufficient.
> 
> But if they are coming from device tree, the device tree developer has
> made an error, which has been silently ignored. Do we want to leave
> the device tree broken? Or should we encourage developers to fix them?
> Printing a warning would facilitate that.

I think that developers should fix the devicetree, so I'll add a warning
message if the specified value exceeds the hardware capability.

Thank you,

---
Best Regards
Kunihiko Hayashi