[Intel-gfx] [RFC 1/4] x86/platform/intel/iosf_mbi: Add a mutex for punit access

Ville Syrjälä ville.syrjala at linux.intel.com
Fri Jan 13 12:20:16 UTC 2017

On Fri, Jan 13, 2017 at 01:12:15PM +0200, Jarkko Nikula wrote:
> On 01/13/2017 12:51 PM, Ville Syrjälä wrote:
> > On Fri, Jan 13, 2017 at 12:34:54PM +0200, Jarkko Nikula wrote:
> >> On 01/13/2017 11:26 AM, Ville Syrjälä wrote:
> >>> It also feels quite hand wavy since the punit could do whatever at
> >>> any time AFAIK. Eg. if there's some thermal event or something the
> >>> punit might kick into action. So trying to protect this from the OS
> >>> side might not be able to avoid these problems entirely. It feels like
> >>> there really should be some kind of shared hardware/firmware mutex
> >>> with the punit to arbitrate access to the i2c bus.
> >>>
> >> There is an HW semaphore for I2C access. It is implemented in
> >> drivers/i2c/busses/i2c-designware-baytrail.c and another set from Hans
> >> is adding support for Cherrytrail into it.
> >
> > Then why do we need anything else?
> >
>  From this patch: "The punit on baytrail / cherrytrail systems is not 
> only accessed through the iosf_mbi functions, but also by the i915 code."

I don't see how that's relevant at all. Multiple things accessing the
punit concurrently should be perfectly fine as long as they don't frob
the same registers.

Ville Syrjälä
Intel OTC

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