Re: [RFC][PATCH 43/43] WIP: drm/i915: Type safe register read/write

Ville Syrjälä
2015-09-24T15:39:13Z

On Wed, Sep 23, 2015 at 05:23:27PM +0200, Daniel Vetter wrote:
> On Fri, Sep 18, 2015 at 08:03:56PM +0300, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Make I915_READ and I915_WRITE more type safe by wrapping the register
> > offset in a struct. This should eliminate most of the fumbles we've had
> > with misplaced parens.
> >
> > This only takes care of normal mmio registers. We could extend the idea
> > to other register types and define each with its own struct. That way
> > you wouldn't be able to accidentally pass the wrong thing to a specific
> > register access function.
> >
> > There are a few uglies left:
> > - switch statements don't like structs as case values, even if
> > you case 'case DEADBEEF.reg:'. Fortunately we don't have too many
> > of those so can maybe switch them to use some port enums or such,
> > or if all else fails if ladders
> > - cmd parser is still iffed out. I was just tool lazy to do that
> > for an RFC
> > - the vgpu stuff is ugly cause I didn't spend any time figuring out
> > what it really wants to do
> > - maybe something else I'm overlooking?
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> I like this very much, which is also why I started pulling in prep patches already.
>
> One bikeshed though: I think this is one of the very few exceptions where
> coding style says typedefs are ok, since this really is just an opaque
> datatype that gets passed around and only opened-up in low-level code
> similar to ptes. So my vote is on i915_reg_t. And since we might want to
> extend this to other register io functions maybe call it i915_mmio_reg_t.

Chris wanted the same, and so I've made the change already. If you want to
take sneak peek, it's available in the update branch I mentioned in my earlier
reply to the cover letter.

--
Ville Syrjälä
Intel OTC