Platform-specific suspend/resume code in drivers

[Alan Stern]

On Wed, 8 Jun 2016, Mason wrote:

> On 07/06/2016 17:06, Alan Stern wrote:
> 
> > On Tue, 7 Jun 2016, Mason wrote:
> >
> >> Another point of confusion for me is this: drivers are supposed to
> >> be shared among platforms, right? So my platform-specific suspend
> >> code should be enabled only if my platform is detected at run-time?
> > 
> > Is your device platform-specific?  If it is then the driver is also
> > platform-specific, and so no part of the driver will be called at
> > runtime unless your platform is detected.
> 
> Specifically, my platform uses
> drivers/net/ethernet/aurora/nb8800.c  => 3 entries in of_match_table.
> drivers/tty/serial/8250/8250_core.c (CONFIG_SERIAL_8250_RT288X variant)
> 
> and also the XHCI USB3 driver, and AHCI SATA driver, wouldn't I need to
> save the context for these too?

Those drivers should already take care of their own contexts.  Is 
there anything platform-specific you need to do in addition?  Consider 
xHCI as an example case -- what more does it need?

> > If the device isn't platform-specific then the driver has to work on a 
> > bunch of different platforms.  It should be written to be 
> > platform-independent as much as possible.
> > 
> >> So this means I need to add in the probe function, for every driver
> >> my platform uses:
> >>
> >>   if (platform == MY_PLATFORM) {
> >>     ops.suspend = my_suspend;
> >>     ops.resume  = my_resume;
> >>   }
> >>
> >> Is that correct?
> > 
> > No.  For one thing, you only have to worry about the 
> > platform-independent drivers -- you know that the platform-specific 
> > ones won't get used unless your platform is present.
> 
> I guess the thermal driver is platform-specific, but most devices
> are third-party IP blocks, so there is a "common" driver upstream.
> But I would need a platform-specific suspend/resume sequence,
> just for my platform.

Why?  What sort of platform-specific things do you need to do?

> > For another, the driver should be written in a way that doesn't require
> > this sort of code.  The ops pointer (not any of the structure's members
> > -- a pointer to the structure) should be set by the platform-dependent
> > part of the driver that handles initialization.
> 
> I don't understand. If my platform loses context on suspend, then
> I must save/restore it. But this wasteful operation should not be
> imposed on other platforms.

More details, please.

Alan Stern