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

Ville Syrjälä
2015-09-28T13:03:14Z

On Mon, Sep 28, 2015 at 03:56:14PM +0300, Jani Nikula wrote:
> On Thu, 24 Sep 2015, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > 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.
>
> You're too fast, making the change already... ;) IMO the shorter the
> better for the common case, and I'd argue we can use i915_reg_t for
> mmio, and something else for the rest.

Easy sed job if we want to go that way.

--
Ville Syrjälä
Intel OTC