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

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Date:   Mon, 20 Apr 2020 08:31:20 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Alan Cooper <alcooperx@...il.com>
Cc:     Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        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 <linux-mmc@...r.kernel.org>,
        ": Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/7] mmc: sdhci: fix base clock usage in preset value

On 17/04/20 4:55 pm, Alan Cooper wrote:
> Acked-by: Al Cooper <alcooperx@...il.com>On Thu, Apr 16, 2020 at 4:27
> AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>
>> 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?
> 
> sdhci_brcmstb_set_clock() assumed that sdhci_calc_clk() would always
> return the divider value without the enable set, so this fixes a case
> for DDR52 where the enable was not being cleared when the divider
> value was changed.
> Acked-by: Al Cooper <alcooperx@...il.com>
> 

That is good to know.  The commit message needs to be updated with that
information, otherwise:

Acked-by: Adrian Hunter <adrian.hunter@...el.com>