linux-kernel - Re: [PATCH 1/2] mmc: sdhci: Add support for setting parent clock

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Date:   Mon, 20 Mar 2017 20:31:20 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        "Ritesh Harjani" <riteshh@...eaurora.org>
CC:     <linux-mmc@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mmc: sdhci: Add support for setting parent clock


On 20/03/17 19:22, Adrian Hunter wrote:
> On 03/16/2017 12:32 PM, Jon Hunter wrote:
>> It is common for SD/MMC host controllers to set the parent clock that
>> drives the SD/MMC interface in order to support various operating
>> speeds. Typically, this is performed by calling common clock framework
>> APIs such as clk_set_rate(). The problem is that these APIs may sleep
>> and must not be called from within atomic sections and therefore, these
>> functions cannot be called within the existing 'set_clock' SDHCI
>> operator because they are called from within the context of a spinlock.
>> Add a new 'set_parent_clock' operator for the SDHCI driver that is
>> called early during the SDHCI 'set_ios' before the spinlock is aquire to
>> give the platform driver the opportunity to set the parent clock rate.
> 
> I just posted a patch to remove the spin lock from set_ios().  Does that help?

Yes it does, thanks!

Technically, the only other place this could occur is in
sdhci_request_done() because this also calls ->set_clock() with the
spinlock held. However, this is only called if
SDHCI_QUIRK_CLOCK_BEFORE_RESET is set, which is only currently true for
a device in sdhci-pci-core.c and this one just uses the normal
sdhci_set_clock() routine. 	

Cheers
Jon

-- 
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