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

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

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 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.