linux-kernel - Re: [PATCH] spi: Limit the spi device max speed to controller's max speed

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Message-ID: <20201209195420.GD4790@sirena.org.uk>
Date:   Wed, 9 Dec 2020 19:54:20 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi: Limit the spi device max speed to controller's max
 speed

On Wed, Dec 09, 2020 at 10:46:36PM +0300, Serge Semin wrote:

> On Wed, Dec 09, 2020 at 07:35:14PM +0200, Tudor Ambarus wrote:

> > Make sure the max_speed_hz of spi_device does not override
> > the max_speed_hz of controller.

> I have doubts that's right thing to do. It seems better to let
> the controller driver to handle the speed clamping itself, while
> to leave the SPI client device max_speed_hz field describing the
> device speed capability. Moreover the SPI-transfers passed to the
> controller will have a SPI-bus speed fixed in accordance with the
> controller and client device capabilities anyway.
> See the __spi_validate() method for details:
> https://elixir.bootlin.com/linux/v5.10-rc7/source/drivers/spi/spi.c#L3570

Right, in general we aim to do this sort of fixup on the transfers
and messages rather than the devices, I guess we might be missing
validation in some of the flash acceleration paths or was this an issue
seen through inspection?

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