linux-kernel - Re: [PATCH v2] soc: qcom: do not disable the iface clock in probe

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Date:	Tue, 23 Sep 2014 21:39:05 -0700
From:	Olof Johansson <olof@...om.net>
To:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:	khilman@...aro.org, arm@...nel.org, agross@...eaurora.org,
	galak@...eaurora.org, linux-arm-kernel@...ts.infradead.org,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] soc: qcom: do not disable the iface clock in probe

On Tue, Sep 23, 2014 at 08:20:54PM +0100, Srinivas Kandagatla wrote:
> since commit 31964ffebbb9 ("tty: serial: msm: Remove direct access to GSBI")'
> serial hangs if earlyprintk are enabled.
> 
> This hang is noticed only when the GSBI driver is probed and all the
> earlyprintks before gsbi probe are seen on the console.
> The reason why it hangs is because GSBI driver disables hclk in its
> probe function without realizing that the serial IP might be in use by
> a bootconsole. As gsbi driver disables the clock in probe the
> bootconsole locks up.
> 
> Turning off hclk's could be dangerous if there are system components
> like earlyprintk using the hclk.
> 
> This patch fixes the issue by delegating the clock management to
> probe and remove functions in gsbi rather than disabling the clock in probe.
> 
> More detailed problem description can be found here:
> http://www.spinics.net/lists/linux-arm-msm/msg10589.html
> 
> Tested-by: Linus Walleij <linus.walleij@...aro.org>
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> ---
> Hi Kevin, 
> 
> Am resending this patch with reference to the problem and adding more
> details to the log.
> 
> Could you pick this fix for the next rc, as this fixes a serial console
> hang with earlyprintk on SOCs like APQ8064.
> 
> Changes since v1:
> 	- added more info in the change log as requested by Kumar and Kevin.

Applied to fixes.


-Olof
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