Re: [PATCH v5 1/3] mfd: Add realtek USB card reader driver

[Roger]

On 03/28/2014 04:31 PM, Oliver Neukum wrote:
> On Fri, 2014-03-28 at 11:33 +0800, Roger wrote:
> > On 03/26/2014 10:36 PM, Oliver Neukum wrote:
> > > On Tue, 2014-03-25 at 18:44 +0800, rogerable@xxxxxxxxxxx wrote:
> > > > From: Roger Tseng <rogerable@xxxxxxxxxxx>
>
> > > > +	if (ret)
> > > > +		goto out_init_fail;
> > > > +
> > > > +	/* initialize USB SG transfer timer */
> > > > +	init_timer(&ucr->sg_timer);
> > > > +	setup_timer(&ucr->sg_timer, rtsx_usb_sg_timed_out, (unsigned long) ucr);
> > > > +#ifdef CONFIG_PM
> > > > +	intf->needs_remote_wakeup = 1;
> > >
> > > Why?
> > Our reader supports remote wake-up from card slot event(insertion,
> > removal). It should be enabled to let the driver be able to detect the
> > newly inserted card.
>
> Interesting. This capability has been lacking for a long time.
> That is cool hardware. Are you sure the upper layers implement
> the event infrastructure so that devices are not polled?
Polling is still necessary because USB essentially doesn't support 
interrupt.

However, if remote wake-up is not enabled or supported, the device will 
have to be resumed every time when polling and then suspended right away 
if there isn't a new card. This should consume more power than the 
designed behavior: suspending device while card removed, taking failed 
polls as no-card, and card being successfully polled after 
insertion-triggered remote wake-up.

> > The LED is not in a permanent cut-off state after here. It is called to
> > guarantee the LED is off during suspend to save more power. It could be
> > lit up in the card host drivers(e.g. rtsx_usb_sdmmc.c) anytime whenever
> > necessary.
> >
> > This has been asked may times. I'm considering putting some comment in
> > next revision.
>
> Good idea.
>
> 	Regards
> 		Oliver

Best regards,
Roger Tseng
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