Re: [PATCH] drm/panfrost: Add PANFROST_BO_NO{READ,WRITE} flags

[Alyssa Rosenzweig <alyssa@collabora.com>]

> > > +	/* Executable implies readable */
> > > +	if ((args->flags & PANFROST_BO_NOREAD) &&
> > > +	    !(args->flags & PANFROST_BO_NOEXEC))
> > > +		return -EINVAL;  
> > 
> > Generally, executable also implies not-writeable. Should we check that?
> 
> We were allowing it until now, so doing that would break the backward
> compat, unfortunately.

Not a problem if you only enforce this starting with the appropriate
UABI version, but...

> Steve also mentioned that the DDK might use shaders modifying other
> shaders here [1]

What? I believe it, but what?

For the case of pilot shaders, that shouldn't require self-modifying
code. As I understand, the DDK binds the push uniform (FAU / RMU) buffer
as global shader memory (SSBO) and uses regular STORE instructions on
it. That requires writability on that BO but that should be fine.