linux-kernel - Re: [PATCH 1/7] mmc: sdhci: fix base clock usage in preset value

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Message-ID: <57b494b8-cae9-df10-2a4d-db02e7212f23@intel.com>
Date:   Thu, 16 Apr 2020 11:26:41 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Kevin Liu <kliu5@...vell.com>,
        Michal Simek <michal.simek@...inx.com>,
        Suneel Garapati <suneel.garapati@...inx.com>,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Al Cooper <alcooperx@...il.com>
Subject: Re: [PATCH 1/7] mmc: sdhci: fix base clock usage in preset value

On 15/04/20 7:28 pm, Michał Mirosław wrote:
> On Wed, Apr 15, 2020 at 03:25:52PM +0300, Adrian Hunter wrote:
>> On 2/04/20 2:54 pm, Michał Mirosław wrote:
>>> Fixed commit added an unnecessary read of CLOCK_CONTROL. The value read
>>> is overwritten for programmable clock preset, but is carried over for
>>> divided clock preset. This can confuse sdhci_enable_clk() if the register
>>> has enable bits set for some reason at time time of clock calculation.
>>> value to be ORed with enable flags. Remove the read.
>>
>> The read is not needed, but drivers usually manage the enable bits,
>> especially disabling the clock before changing the frequency.  What driver
>> is it?
> 
> Hopefully no driver requires this. It's just removing a trap.

The only driver that looks like it would benefit is sdhci-brcmstb because it
does not clear enable bits in sdhci_brcmstb_set_clock().  Adding Al Cooper.
Al, can you ack this?