linux-kernel - Re: [PATCHv4 2/4] serial: imx: add runtime pm support

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Message-id: <2095117.mcCCLIRizo@amdc1976>
Date:	Mon, 17 Aug 2015 17:40:59 +0200
From:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:	Eduardo Valentin <edubezval@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Fabio Estevam <festevam@...il.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Linux PM <linux-pm@...r.kernel.org>,
	linux-serial@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv4 2/4] serial: imx: add runtime pm support


Hi,

On Friday, August 14, 2015 09:37:46 PM Eduardo Valentin wrote:
> This change introduces the runtime pm support on imx serial
> driver. The objective is to be able to idle the uart
> port whenever it is not in use while still being able
> to wake it up when needed. The key changes in this patch are:
> 1. Move the clock handling to runtime pm. Both, ipg and per,
> are now handled in the suspend and resume callbacks. Only
> enabling and disabling the clocks are handled in runtime
> suspend and resume, so we are able to use runtime pm
> in IRQ context.
> 2. Clocks are prepared in probe and unprepared in remove,
> so we do not need to prepare (may sleep) in runtime pm.
> 3. We mark the device activity based on uart and console
> callbacks. Whenever the device is needed and we want to
> access registers, we runtime_pm_get and then mark its
> last usage when we are done. This is done also across
> IRQs and DMA callbacks.
> 4. We reuse the infrastructure in place for suspend and
> resume, so we do not need to redo wakeup configuration,
> or context save and restore.
> 
> After this change, the clocks are still sane, in the sense
> of having balanced clock prepare and enable.

The clock changes in this patch seem to make this driver
non-functional with CONFIG_PM=n.  Have you tested your
changes with CONFIG_PM=n?

Generally the driver should not depend on PM support to
enable its clocks.  We had this issue in few Exynos-specific
drivers not that long time ago..

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

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