From: Doug Anderson <dianders@chromium.org>
To: Seungwon Jeon <tgih.jun@samsung.com>
Cc: Chris Ball <cjb@laptop.org>, Olof Johansson <olof@lixom.net>,
Jaehoon Chung <jh80.chung@samsung.com>,
James Hogan <james.hogan@imgtec.com>,
Grant Grundler <grundler@chromium.org>,
Alim Akhtar <alim.akhtar@samsung.com>,
Abhilash Kesavan <a.kesavan@samsung.com>,
Tomasz Figa <tomasz.figa@gmail.com>,
"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 3/4] mmc: dw_mmc: Always setup the bus after suspend/resume
Date: Fri, 9 Aug 2013 08:43:13 -0700 [thread overview]
Message-ID: <CAD=FV=VO=50uMXfwY5iNa+xiamRiHTSpTMXs+EdMeUTawkeyqw@mail.gmail.com> (raw)
In-Reply-To: <001a01ce9505$59c28b20$0d47a160$%jun@samsung.com>
Seungwon,
On Fri, Aug 9, 2013 at 6:35 AM, Seungwon Jeon <tgih.jun@samsung.com> wrote:
> On Wed, August 07, 2013, Doug Anderson wrote:
>> After suspend/resume all of the dw_mmc registers are reset to
>> defaults. We restore most of them, but specifically don't setup the
>> clock registers after resume unless we've got a powered card. Things
>> still work because the core will eventually call set_ios() and we'll
>> set things up.
>
> Hmm, I didn't get the need of this call during resume.
> I think set_ios is only valid where core layer calls.
> Besides, important things is ios's parameters.
> If suspend has finished successfully, last call of set_ios() is from mmc_power_off().
> On seeing fields of 'mmc->ios' stored last, these values aren't proper in resume phase.
> Please check mmc_power_off() function.
> In case MMC_PM_KEEP_POWER it could be kept.
Most of my reasoning has to do with the fact that the state of the
system after suspend/resume should not be significantly different than
the state of the system before suspend/resume. If the state of the
system is different in the two cases it points out potential problems
or inefficiencies.
To make this more concrete:
1. Boot up a system with no card in the SD Card slot.
2. Note down the value of registers like CLKDIV, CLKENA, etc.
3. Suspend / resume (S2R)
4. Check the values of CLKDIV, CLKENA, etc.
You will notice that they are different. This is a bad sign and can
be a source of bugs (though I don't know of any). ...or it could mean
that power draw is different (could be better, could be worse) after a
suspend/resume cycle.
Said another way, if the value of CLKDIV, CLKENA, etc is not important
when a card is not inserted, why do they get initialized at boot time?
In general, I think that the mmc core code makes the assumption that
it's up to the driver to make sure that its state is preserved across
S2R. For dw_mmc the driver doesn't do the "brute force" that some
drivers do of just saving and restoring all registers using a copy
loop. Instead, the dw_mmc driver runs code that tries to set the
state back to something reasonable. Without my patch the dw_mmc
driver doesn't run any code that restores these registers.
dw_mci_set_ios() will do so.
Another option would be to forcibly save/restore registers in suspend/resume.
-Doug
next prev parent reply other threads:[~2013-08-09 15:43 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-09 17:31 [PATCH 0/5] mmc: dw_mmc: fixes for suspend/resume on exynos Doug Anderson
2013-07-09 17:31 ` [PATCH 1/5] mmc: dw_mmc: Invalidate cache of current_speed after suspend/resume Doug Anderson
2013-07-09 17:31 ` [PATCH 2/5] mmc: dw_mmc: Add suspend/resume callbacks; disable irq during suspend Doug Anderson
2013-07-09 21:17 ` James Hogan
2013-07-09 21:31 ` Doug Anderson
2013-07-09 17:31 ` [PATCH 3/5] mmc: dw_mmc: Add exynos resume callback to clear WAKEUP_INT Doug Anderson
2013-07-09 19:09 ` Doug Anderson
2013-07-11 0:43 ` Grant Grundler
2013-07-09 17:31 ` [PATCH 4/5] mmc: dw_mmc: Always setup the bus after suspend/resume Doug Anderson
2013-07-09 17:31 ` [PATCH 5/5] mmc: dw_mmc: Set timeout to max upon resume Doug Anderson
2013-07-09 23:19 ` [PATCH v2 0/5] mmc: dw_mmc: fixes for suspend/resume on exynos Doug Anderson
2013-07-09 23:19 ` [PATCH v2 1/5] mmc: dw_mmc: Invalidate cache of current_speed after suspend/resume Doug Anderson
2013-07-09 23:19 ` [PATCH v2 2/5] mmc: dw_mmc: Add suspend_noirq/resume_noirq callbacks for dw_mmc-pltfm Doug Anderson
2013-07-10 8:37 ` James Hogan
2013-07-10 15:08 ` Doug Anderson
2013-07-09 23:19 ` [PATCH v2 3/5] mmc: dw_mmc: Add exynos resume_noirq callback to clear WAKEUP_INT Doug Anderson
2013-07-10 14:54 ` Seungwon Jeon
2013-07-10 15:05 ` Doug Anderson
2013-07-15 12:09 ` Seungwon Jeon
2013-07-31 16:18 ` Doug Anderson
2013-08-06 21:36 ` Doug Anderson
2013-07-09 23:19 ` [PATCH v2 4/5] mmc: dw_mmc: Always setup the bus after suspend/resume Doug Anderson
2013-07-09 23:19 ` [PATCH v2 5/5] mmc: dw_mmc: Set timeout to max upon resume Doug Anderson
2013-07-10 14:54 ` Seungwon Jeon
2013-07-10 15:42 ` [PATCH v3 0/5] mmc: dw_mmc: fixes for suspend/resume on exynos Doug Anderson
2013-07-10 15:42 ` [PATCH v3 1/5] mmc: dw_mmc: Invalidate cache of current_speed after suspend/resume Doug Anderson
2013-07-10 15:42 ` [PATCH v3 2/5] mmc: dw_mmc: Add suspend_noirq/resume_noirq callbacks for dw_mmc-pltfm Doug Anderson
2013-07-15 12:09 ` Seungwon Jeon
2013-08-06 21:32 ` Doug Anderson
2013-07-10 15:42 ` [PATCH v3 3/5] mmc: dw_mmc: Add exynos resume_noirq callback to clear WAKEUP_INT Doug Anderson
2013-07-16 1:36 ` Jaehoon Chung
2013-07-10 15:42 ` [PATCH v3 4/5] mmc: dw_mmc: Always setup the bus after suspend/resume Doug Anderson
2013-07-10 15:42 ` [PATCH v3 5/5] mmc: dw_mmc: Set timeout to max upon resume Doug Anderson
2013-08-06 21:37 ` [PATCH v4 0/4] mmc: dw_mmc: fixes for suspend/resume on exynos Doug Anderson
2013-08-06 21:37 ` [PATCH v4 1/4] mmc: dw_mmc: Invalidate cache of current_speed after suspend/resume Doug Anderson
2013-08-06 21:58 ` Tomasz Figa
2013-08-08 5:14 ` Jaehoon Chung
2013-08-09 13:32 ` Seungwon Jeon
2013-08-09 15:22 ` Doug Anderson
2013-08-12 7:14 ` Seungwon Jeon
2013-08-22 0:54 ` Doug Anderson
2013-08-22 16:25 ` Doug Anderson
2013-08-06 21:37 ` [PATCH v4 2/4] mmc: dw_mmc: Add exynos resume_noirq callback to clear WAKEUP_INT Doug Anderson
2013-08-06 21:58 ` Tomasz Figa
2013-08-06 22:09 ` Doug Anderson
2013-08-06 22:20 ` Tomasz Figa
2013-08-09 13:33 ` Seungwon Jeon
2013-08-09 15:05 ` Doug Anderson
2013-08-06 21:37 ` [PATCH v4 3/4] mmc: dw_mmc: Always setup the bus after suspend/resume Doug Anderson
2013-08-06 22:01 ` Tomasz Figa
2013-08-09 13:35 ` Seungwon Jeon
2013-08-09 15:43 ` Doug Anderson [this message]
2013-08-12 7:20 ` Seungwon Jeon
2013-08-06 21:37 ` [PATCH v4 4/4] mmc: dw_mmc: Set timeout to max upon resume Doug Anderson
2013-08-06 22:02 ` Tomasz Figa
2013-08-09 16:33 ` [PATCH v5 0/4] mmc: dw_mmc: fixes for suspend/resume on exynos Doug Anderson
2013-08-09 16:33 ` [PATCH v5 1/4] mmc: dw_mmc: Invalidate cache of current_speed after suspend/resume Doug Anderson
2013-08-09 16:33 ` [PATCH v5 2/4] mmc: dw_mmc: Add exynos resume_noirq callback to clear WAKEUP_INT Doug Anderson
2013-08-09 16:41 ` Fabio Estevam
2013-08-09 16:48 ` Doug Anderson
2013-08-12 7:21 ` Seungwon Jeon
2013-08-09 16:33 ` [PATCH v5 3/4] mmc: dw_mmc: Always setup the bus after suspend/resume Doug Anderson
2013-08-09 16:33 ` [PATCH v5 4/4] mmc: dw_mmc: Set timeout to max upon resume Doug Anderson
2013-08-21 11:48 ` [PATCH v5 0/4] mmc: dw_mmc: fixes for suspend/resume on exynos Seungwon Jeon
2013-08-21 15:13 ` Doug Anderson
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