Re: [PATCH] mmc: core: Mark mmc_host device with pm_runtime_no_callbacks

[Ulf Hansson]

On Tue, 23 Mar 2021 at 15:00, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>
> On Tue, 23 Mar 2021 at 11:49, hieagle <chgokhl@xxxxxxxxx> wrote:
> >
> > We encounter a resume issue in our device sometimes. The mmc device's
> > parent list is
> > mmc0:0001->mmc_host mmc0->fa630000.mmc->soc in our soc. We found in the blow
> > case with mmc0->power.disable_depth=0 the mmc_runtime_resume will be skipped,
> > which cause subsequent mmc command fail.
> >
> > mmc_get_card(mmc0:0001)->pm_runtime_get_sync->rpm_resume(mmc0:0001)->rpm_resume(mmc0)
> > The rpm_resume(mmc0) return -ENOSYS due to no callback and
> > mmc0->power.runtime_status
> > keep RPM_SUSPENDED. This lead to rpm_resume(mmc0:0001) return -EBUSY and skip
> > rpm_callback which call mmc_runtime_resume, the mmc is still in
> > suspended and the
> > subsequent mmc command fail.
> >
> > [  198.856157] Call trace:
> > [  198.858917] [<ffffff800808bd9c>] dump_backtrace+0x0/0x1cc
> > [  198.864966] [<ffffff800808bf7c>] show_stack+0x14/0x1c
> > [  198.870627] [<ffffff8008400e88>] dump_stack+0xa8/0xe0
> > [  198.876288] [<ffffff800854d38c>] rpm_resume+0x850/0x938
> > [  198.882141] [<ffffff800854cd8c>] rpm_resume+0x250/0x938
> > [  198.887994] [<ffffff800854d4c4>] __pm_runtime_resume+0x50/0x74
> > [  198.894530] [<ffffff80087b9e64>] mmc_get_card+0x3c/0xb8
> > [  198.900388] [<ffffff80087cd2e0>] mmc_blk_issue_rq+0x2b0/0x4d8
> > [  198.906824] [<ffffff80087cd5e4>] mmc_queue_thread+0xdc/0x198
> > [  198.913165] [<ffffff80080d4b2c>] kthread+0xec/0x100
> > [  198.918632] [<ffffff8008083890>] ret_from_fork+0x10/0x40
> > [  198.924582] mmc0  callback           (null)
> > [  198.935837] mmcblk mmc0:0001: __pm_runtime_resume ret -16
> >
> > Mark mmc_host device with pm_runtime_no_callbacks will solve the issue.
> > Thanks.
> > Huanlin Ke

So I have looked a bit closer to this, finally. Apologies for the delay.

If I am not mistaken, rpm_resume() should *not* be called recursively
for a device's parent, unless the parent's ->power.disable_depth has
been decremented to zero. No matter if we have called
pm_runtime_no_callbacks() for the child device or not.

In the scenario you describe, the parent device corresponds to the mmc
class device (initialized in mmc_alloc_host()). Since the mmc core
never calls pm_runtime_enable() for it, its - >power.disable_depth
should always remain greater than 0.

Although, I admit, the code in runtime.c isn't that easy to browse, so
I may be wrong. That said, I fail to see how -ENOSYS can be returned
rpm_resume() in the path you describe.

Would it be possible for you to provide more logs to show this?

Or could it be that you have a patch locally that calls
pm_runtime_enable() for the mmc class device, somewhere? That would
also explains things? :-)

[...]

> > >
> > > On Sat, 20 Mar 2021 at 05:57, kehuanlin <chgokhl@xxxxxxxxx> wrote:
> > > >
> > > > The rpm_resume() will call parent's resume callback recursively.
> > > > Since mmc_host has no its own pm_runtime callbacks, the mmc devices
> > > > may fail to resume (-ENOSYS in rpm_callback) sometimes. Mark mmc_host
> > > > device with pm_runtime_no_callbacks can fix the issue.
> > >
> > > Can you please elaborate more on this? What do you mean by "sometimes"?
> > >
> > > More precisely, how do you trigger the rpm_callback() for mmc class
> > > device to return -ENOSYS?
> > >
> > > Don't get me wrong, the patch is fine, but I want to understand if it
> > > actually solves a problem for you - or that it's better considered as
> > > an optimization?
> > >
> > > Kind regards
> > > Uffe
> > >
> > > >
> > > > Signed-off-by: kehuanlin <chgokhl@xxxxxxxxx>
> > > > ---
> > > >  drivers/mmc/core/host.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> > > > index 9b89a91b6b47..177bebd9a6c4 100644
> > > > --- a/drivers/mmc/core/host.c
> > > > +++ b/drivers/mmc/core/host.c
> > > > @@ -15,6 +15,7 @@
> > > >  #include <linux/of.h>
> > > >  #include <linux/of_gpio.h>
> > > >  #include <linux/pagemap.h>
> > > > +#include <linux/pm_runtime.h>
> > > >  #include <linux/pm_wakeup.h>
> > > >  #include <linux/export.h>
> > > >  #include <linux/leds.h>
> > > > @@ -480,6 +481,7 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
> > > >         host->class_dev.class = &mmc_host_class;
> > > >         device_initialize(&host->class_dev);
> > > >         device_enable_async_suspend(&host->class_dev);
> > > > +       pm_runtime_no_callbacks(&host->class_dev);
> > > >
> > > >         if (mmc_gpio_alloc(host)) {
> > > >                 put_device(&host->class_dev);
> > > > --
> > > > 2.30.0
> > > >

Kind regards
Uffe