Hi,
On Fri, Aug 19, 2011 at 04:48:52PM -0600, Paul Walmsley wrote:
>
> After commit 665d001338b494d6d62810aa99b4c0fa1a0884b9 ("OMAP2+: hwmod:
> Follow the recommended PRCM module enable sequence"), device drivers
> for OMAP IP blocks that do not use runtime PM can cause oopses or
> kernel instability[1][2].
>
> This is because those non-runtime PM drivers do not use the hwmod
> code, which implements the correct IP block enable and disable
> sequence.
>
> Several options for dealing with this problem have been proposed:
>
> 1. Add a new field to the OMAP struct clk to mark clocks that are
> currently used by non-runtime PM drivers. Modify the clock code to
> use the old clockdomain sequence for these marked clocks. As
> drivers are converted to use runtime PM, remove the annotation from
> the clocks.
>
> 2. Similar to #1, but associate the flag with the struct omap_clk
> instead.
>
> 3. Add IDLEST wait support to the OMAP4 clock code, similar to the way
> it is implemented for OMAP2/3, and enable it in each struct clk
> currently used by non-runtime PM drivers. As drivers are converted
> to use runtime PM, remove the annotation from the clocks.
>
> 4. Do nothing; leave the problem to those responsible for the
> unconverted drivers.
>
> 5. Re-enable clock-based clockdomain control in the OMAP4 clock code.
> This would revert back to the behavior of Linux 3.0, simply with a
> slightly longer module enable/disable latency.
>
> Unfortunately, no approach seemed particularly good. Options 1
> through 3 seemed unwise due to the following reasons:
>
> A. The OMAP struct clks are intended primarily to describe hardware
> clock nodes, and the intention is that no driver-specific data
> should be stored there (applies to #1)
>
> B. The resulting patch would have been quite large for the -rc series
> (applies to #1, #2, #3)
>
> C. The patch would have been a new, yet temporary hack; and similar fixes
> have drawn negative comments in the recent past (see for example [3])
>
> Option 4 is undesirable because commit
> 665d001338b494d6d62810aa99b4c0fa1a0884b9 ("OMAP2+: hwmod: Follow the
> recommended PRCM module enable sequence") has resulted in a less
> stable kernel; and kernel stability is more important than OMAP4 power
> management.
>
> Option 5 is the approach taken in this patch. This seemed to be the
> least intrusive approach for 3.1-rc.
>
> The approach in this patch was originally proposed by Ohad Ben-Cohen
> <ohad@xxxxxxxxxx>. I'm simply writing the commit message and passing
> it along.
>
> ...
>
> Thanks to Luciano Coelho <coelho@xxxxxx> for reporting the problem.
> Thanks to Ohad Ben-Cohen <ohad@xxxxxxxxxx> for tracking the problem
> down, generating a temporary workaround, and proposing a patch to deal
> with the problem. Thanks to Rajendra Nayak <rnayak@xxxxxx> for
> proposing another patch to deal with the problem.
>
> This patch is intended for the 3.1-rc fixes series.
>
> 1. Coelho, Luciano <coelho@xxxxxx>. _Re: Oops on ehci_hcd when
> booting 3.0.0-rc2 on panda_. Tue, 09 Aug 2011 14:26:08 +0300.
> Posted to the <linux-omap@xxxxxxxxxxxxxxx> mailing list. Available
> from (among others)
> http://www.spinics.net/linux/lists/linux-omap/msg55213.html
>
> 2. Munegowda, Keshava <keshava_mgowda@xxxxxx>. _Re: Oops on ehci_hcd
> when booting 3.0.0-rc2 on panda_. Thu, 11 Aug 2011 13:51:05 +0530.
> Posted to the <linux-omap@xxxxxxxxxxxxxxx> mailing list. Available
> from (among others)
> http://www.spinics.net/linux/lists/linux-omap/msg55371.html
>
> 3. King, Russell <linux@xxxxxxxxxxxxxxxx>. _Re: [PATCH 5/8] OMAP4:
> PM: TEMP: Prevent l3init from idling/force sleep_. Thu, 23 Jun
> 2011 16:22:49 +0100. Posted to the <linux-omap@xxxxxxxxxxxxxxx>
> mailing list. Available from (among others)
> http://www.mail-archive.com/linux-omap@xxxxxxxxxxxxxxx/msg51392.html
>
> Signed-off-by: Paul Walmsley <paul@xxxxxxxxx>
> Cc: Luciano Coelho <coelho@xxxxxx>
> Cc: Ohad Ben-Cohen <ohad@xxxxxxxxxx>
> Cc: Rajendra Nayak <rnayak@xxxxxx>
> Cc: Benoît Cousson <b-cousson@xxxxxx>
> ---
> arch/arm/mach-omap2/clock44xx_data.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/arm/mach-omap2/clock44xx_data.c b/arch/arm/mach-omap2/clock44xx_data.c
> index 2af0e3f..fe6508d 100644
> --- a/arch/arm/mach-omap2/clock44xx_data.c
> +++ b/arch/arm/mach-omap2/clock44xx_data.c
> @@ -3379,7 +3379,7 @@ int __init omap4xxx_clk_init(void)
> }
>
> clk_init(&omap2_clk_functions);
maybe add a comment here stating why this line is commented out ?
> - omap2_clk_disable_clkdm_control();
> + /* omap2_clk_disable_clkdm_control(); */
>
> for (c = omap44xx_clks; c < omap44xx_clks + ARRAY_SIZE(omap44xx_clks);
> c++)
--
balbi
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