Re: [PATCH v4 2/4] mmc: tmio: Add tuning support

[Simon Horman <horms@verge.net.au>]

On Thu, Sep 01, 2016 at 08:46:44AM +0200, Simon Horman wrote:
> On Wed, Aug 31, 2016 at 09:38:40AM +0200, Ulf Hansson wrote:
> > On 30 August 2016 at 22:51, Simon Horman <horms@verge.net.au> wrote:
> > > On Mon, Aug 29, 2016 at 04:05:55PM +0200, Ulf Hansson wrote:
> > >> On 29 August 2016 at 14:05, Simon Horman <horms@verge.net.au> wrote:
> > >> > On Fri, Aug 26, 2016 at 10:01:35AM +0200, Ulf Hansson wrote:
> > >> >> On 25 August 2016 at 14:04, Simon Horman <horms@verge.net.au> wrote:
> > >> >> > On Tue, Aug 23, 2016 at 05:02:56PM +0200, Ulf Hansson wrote:
> > >> >
> > >> > ...
> > >
> > > ...
> > >
> > >> > @@ -1271,6 +1278,7 @@ int tmio_mmc_host_runtime_suspend(struct device *dev)
> > >> >
> > >> >         mmc_retune_timer_stop(host->mmc);
> > >> >         mmc_retune_needed(host->mmc);
> > >> > +       host->use_saved_taps = true;
> > >>
> > >> I don't think you should trigger a re-tune here at all. Moreover you
> > >> don't need to keep track of whether you have valid tap values by using
> > >> the ->use_saved_taps variable, the mmc core deals with this for you.
> > >>
> > >> Instead, you should restore the tap values by invoking
> > >> host->select_tuning() from the ->runtime_resume() callback, although
> > >> only when host->mmc->can_retune == 1. We should probably add a helper
> > >> function in the mmc core for this check, instead of accessing
> > >> "can_retune" directly.
> > >
> > > Thanks, I was wondering what the best way to handle this is.
> > >
> > > I tried your suggestion above but it seems that host->mmc->can_retune is
> > > zero when ->runtime_resume() is called because of the following call paths:
> > >
> > > a) _mmc_sd_suspend()
> > >      -> mmc_power_off()
> > >         -> mmc_set_initial_state()
> > >            -> mmc_retune_disable
> > >    and
> > > b) mmc_sd_runtime_resume()
> > >      -> mmc_power_up
> > >         -> mmc_set_initial_state()
> > >            -> mmc_retune_disable
> > >
> > >> >         tmio_mmc_disable_mmc_irqs(host, TMIO_MASK_ALL);
> > 
> > This is exactly what shall happen :-)
> > 
> > If the mmc core suspends the card, it means it will also re-initialize
> > the card when resuming it. In that way the regular tuning sequence
> > will take place as a part of re-initialization of the card, so you
> > definitely must not restore tap values in these case. That is why you
> > should be using the can_retune to know when to restore the values.
> 
> Understood. In that case things are working as expected.

I do have one question. It seems to me that  host->mmc->can_retune == 1 on
resume. If so, when would the saved tap values be used?  I feel that I am
missing something here.

> > > I plan to repost this patchset without the tap restoration code.
> > > This is because I have a number of changes locally, in particular
> > > to address other parts of your review, and I would like
> > > them to see the light of day.
> > >
> > > I will mark the tap restoration as a TODO item which we can address
> > > before merging the code in question.
> > 
> > It shouldn't be that hard to implement this, so I rather see that we
> > get this right from the beginning.
> > 
> > As matter of fact it probably requires less code than you had in your
> > initial approach, especially since I don't think you need to deal with
> > anything tuning related in the ->runtime_suspend() callback, but only
> > in ->runtime_resume().
> 
> Got it.