Re: [PATCH V7 3/4] drm/bridge: Add driver for GE B850v3 LVDS/DP++ Bridge

[Archit Taneja]

On 01/30/2017 10:35 PM, Jani Nikula wrote:
> On Sat, 28 Jan 2017, Peter Senna Tschudin <peter.senna@xxxxxxxxxxxxx> wrote:
> > On Thu, Jan 05, 2017 at 01:18:47PM +0530, Archit Taneja wrote:
> > Hi Archit,
> >
> > Thank you for the comments!
> >
> > [...]
> > > > +	total_size = (block[EDID_EXT_BLOCK_CNT] + 1) * EDID_LENGTH;
> > > > +	if (total_size > EDID_LENGTH) {
> > > > +		kfree(block);
> > > > +		block = kmalloc(total_size, GFP_KERNEL);
> > > > +		if (!block)
> > > > +			return NULL;
> > > > +
> > > > +		/* Yes, read the entire buffer, and do not skip the first
> > > > +		 * EDID_LENGTH bytes.
> > > > +		 */
> > >
> > > Is this the reason why you aren't using drm_do_get_edid()?
> >
> > Yes, for some hw specific reason, it is necessary to read the entire
> > EDID buffer starting from 0, not block by block.
>
> Hrmh, I'm planning on moving the edid override and firmware edid
> mechanisms at the drm_do_get_edid() level to be able to truly and
> transparently use a different edid. Currently, they're only used for
> modes, really, and lead to some info retrieved from overrides, some from
> the real edid. This kind of hacks will bypass the override/firmware edid
> mechanisms then too. :(

It seems like there is a HW issue which prevents them from reading EDID
from an offset. So, I'm not sure if it is a hack or a HW limitation.

One way around this would be to hide the HW requirement in the
get_edid_block func pointer passed to drm_do_get_edid(). This
would, however, result in more i2c reads (equal to # of extension
blocks) than what the patch currently does.

Peter, if you think doing extra EDID reads isn't too costly on your
platform, you could consider using drm_do_get_edid(). If not, I guess
you'll miss out on the additional functionality Jani is going to add
in the future.

Thanks,
Archit


> BR,
> Jani.
>
>
> > [...]
> >
> > I fixed all your other suggestions. Thank you!
> > _______________________________________________
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> > dri-devel@xxxxxxxxxxxxxxxxxxxxx
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