Re: [PATCH v4 10/14] mfd: lm3533: Set DMA mask

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Wed, Jun 10, 2026 at 05:40:56PM +0300, Svyatoslav Ryhel wrote:
> вт, 9 черв. 2026 р. о 22:17 Andy Shevchenko <andriy.shevchenko@intel.com> пише:
> > On Sat, Jun 06, 2026 at 07:57:34AM +0300, Svyatoslav Ryhel wrote:
> > > Missing coherent_dma_mask assigning triggers the following warning in
> > > dmesg:
> > >
> > > [    3.287872] platform lm3533-backlight.0: DMA mask not set
> > >
> > > Since this warning might be elevated to an error in the future, set
> > > coherent_dma_mask to zero because both the core and cells do not utilize
> > > DMA.
> >
> > Hmm... I am not sure about this. The entire kernel has only two drivers that
> > do that, and thanks to their commit messages one of them pointed out to the
> > commit from 2018. So, if no other devices suffer from this, I think it has to
> > be a better way of achieving the same.
> 
> If mfd framework warns that DMA mask is not set then this must be
> addressed. Why then there is such warning at the first place if mask
> can be just skipped. Then warning would be just a debug message. What
> is warning today can become error tomorrow.

It's there for 8 years. And only a few drivers explicitly nullify it.
I think doing this patch one should really understand what's going on.
(Note, I'm not that person, it's my gut feelings based on the experience
 and the above statistics.) MFD creates a lot of platform devices for
which DMA mask is set automatically. So, why is it not set properly for
this device?

-- 
With Best Regards,
Andy Shevchenko