Re: [PATCH v1] spi: add STM32F7 QSPI controller driver

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Oleksij,

On 4/1/25 11:05, Oleksij Rempel wrote:
> On Tue, Apr 01, 2025 at 10:53:44AM +0200, Ahmad Fatoum wrote:
>> Hello Oleksij,
>>
>> On 3/31/25 14:29, Oleksij Rempel wrote:
>>> From: Ahmad Fatoum <a.fatoum@pengutronix.de>
>>>
>>> Introduce support for the STM32F7 QSPI controller, compatible with
>>> "st,stm32f469-qspi".
>>>
>>> Validated on STM32MP133-based MECT1S r1 board, which includes an
>>> F7-compatible QSPI peripheral
>>>
>>> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
>>> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
>>> ---
>>
>> [snip]
>>
>>> +static int stm32_qspi_get_mode(u8 buswidth)
>>
>> Is this ever called with a buswidth > 1? I think the spi_mem core in
>> barebox never uses higher buswidths. Given that you are adding QSPI
>> support, you will surely want to see quad buswidth actually working,
>> right? :D
> 
> Sure :) I get it - every maintainer dreams of getting the most out of
> each patch, and full QSPI support with quad buswidth would definitely be
> nice to have.
> 
> But with this patch, we're going from “doesn't work at all” to “works,
> just not at full speed yet.” That’s already a big step forward,
> especially for bring-up and flashing use cases.

I agree that it's a considerable improvement. Thanks for putting time
into making it work.

> If we judged everything in Barebox by full performance, we’d probably
> have to drop most of the networking drivers too - since Barebox usually
> isn’t about maxing out throughput anyway ;)

Let's get TCP merged before going there. :D

> So yes, proper quad support would be great - but for now, this patch
> gets us something working, and that’s a solid starting point.

The thing is there are a number of QSPI drivers already and there's
still no exercising of higher buswidths. I don't have any projects
currently that use SPI-NOR with a higher bus width, so the only thing I
can do is raise some awareness of the limitation. ;)

Cheers,
Ahmad

> 
> Best Regards,
> Oleksij

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