Hi Vinod,
On Fri, Dec 5, 2014 at 6:47 PM, Vinod Koul <vinod.koul@xxxxxxxxx> wrote:
> On Wed, Nov 19, 2014 at 04:15:46PM +0100, Geert Uytterhoeven wrote:
>> During system reboot, the sh-dma-engine device may be runtime-suspended,
>> causing a crash:
>>
>> Unhandled fault: imprecise external abort (0x1406) at 0x0002c02c
>> Internal error: : 1406 [#1] SMP ARM
>> ...
>> PC is at sh_dmae_ctl_stop+0x28/0x64
>> LR is at sh_dmae_ctl_stop+0x24/0x64
>>
>> If the sh-dma-engine is runtime-suspended, its module clock is turned
>> off, and its registers cannot be accessed. Runtime-resume the device in
>> the driver's .shutdown() callback to fix this.
>>
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
>> ---
>> drivers/dma/sh/shdmac.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/dma/sh/shdmac.c b/drivers/dma/sh/shdmac.c
>> index b65317c6ea4e722c..a13c6ba7468f12a6 100644
>> --- a/drivers/dma/sh/shdmac.c
>> +++ b/drivers/dma/sh/shdmac.c
>> @@ -585,7 +585,10 @@ static void sh_dmae_chan_remove(struct sh_dmae_device *shdev)
>> static void sh_dmae_shutdown(struct platform_device *pdev)
>> {
>> struct sh_dmae_device *shdev = platform_get_drvdata(pdev);
>> +
>> + pm_runtime_get_sync(&pdev->dev);
>> sh_dmae_ctl_stop(shdev);
>> + pm_runtime_put(&pdev->dev);
> but if you are runtime_suspended, then why should you even proceed to stop
> the clock. Why not just cleanup and return when runtime suspended
sh_dmae_ctl_stop() stops the DMA engine, not the clock.
Accessing the DMA engine cannot be done while the module clock is stopped.
If pm_runtime_suspended() returns true, I can indeed just return (no new
request can come in while .shutdown() is called).
However, if pm_runtime_suspended() returns false, the device may still
become runtime suspended in between the check for pm_runtime_suspended()
and accessing the DMA engine registers in sh_dmae_ctl_stop(), as runtime
suspend is an asynchronous operation, right?
So I think adding a check for pm_runtime_suspended() can only serve as
an optimization, the pm_runtime_{get_sync,put}() has to stay to prevent a
race condition.
Please correct me if I'm wrong.
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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