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

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Message-ID: <20201209203042.oqbcijwaxqt5aa7b@mobilestation>
Date:   Wed, 9 Dec 2020 23:30:42 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Mark Brown <broonie@...nel.org>
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 08:25:52PM +0000, Mark Brown wrote:
> On Wed, Dec 09, 2020 at 11:15:35PM +0300, Serge Semin wrote:
> > On Wed, Dec 09, 2020 at 07:54:20PM +0000, Mark Brown wrote:
> 
> > > 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?
> 
> > In case of DW SPI driver we just make sure the SPI-client device
> > speed set in the max_speed_hz doesn't exceed the controller SPI-bus
> > clock frequency and clamp it if it does. So the driver is safe in that
> > matter.
> 

> Ideally the driver wouldn't have to check though (no harm in doing so of
> course).

If so then we'd need to have a dedicated speed-related field in the
spi_mem_op structure, which would be accordingly initialized by the
SPI-mem core.

-Sergey