linux-kernel - Re: [PATCH] spi: meson-spicc: save pow2 datarate between messages

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Date:   Wed, 10 Aug 2022 16:01:33 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Da Xue <da@...re.computer>
Subject: Re: [PATCH] spi: meson-spicc: save pow2 datarate between messages

On 10/08/2022 14:37, Mark Brown wrote:
> On Wed, Aug 10, 2022 at 11:17:14AM +0200, Neil Armstrong wrote:
>> On 09/08/2022 17:27, Mark Brown wrote:
>>> On Tue, Aug 09, 2022 at 05:20:19PM +0200, Neil Armstrong wrote:
> 
>>> When you say the value set by the clock framework does that mean that
>>> the clock driver is adjusting hardware inside the SPI controller IP
>>> block which is then getting reset by the SPI driver without the SPI
>>> driver knowing about it?  That seems like a bad idea as you're finding
>>> here.
> 
>> The SPI driver is explicitely triggering a reset at the end of each message
>> to get back to a clean HW state, but it does reset the content of the "legacy"
>> registers containing the power of 2 divider value, the new registers configuring
>> the new clock divider path (only on newer SoCs) doesn't get cleared.
> 
> Sure, but that doesn't really address the concern - is this something
> that the clk driver programmed or is this the driver forgetting to
> restore a register that it programmed itself?  The commit message sounds
> like the former which is a much bigger problem.

It's what is programmed by the Clock Framework yes, it was designed as-is
so the Clock Framework takes the most accurate clock path but the reset case
wasn't taken in account.

Neil