Re: [Intel-gfx] [PATCH 1/2] drm: Introduce per-device driver_features

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: "Michel Dänzer" <michel@daenzer.net>
Cc: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 1/2] drm: Introduce per-device driver_features
Date: Thu, 13 Sep 2018 18:06:01 +0300	[thread overview]
Message-ID: <20180913150601.GN5565@intel.com> (raw)
In-Reply-To: <cd9c48d4-89a8-f393-b072-efcff1717567@daenzer.net>

On Thu, Sep 13, 2018 at 04:52:34PM +0200, Michel Dänzer wrote:
> On 2018-09-13 4:29 p.m., Ville Syrjälä wrote:
> > On Thu, Sep 13, 2018 at 03:50:01PM +0200, Daniel Vetter wrote:
> >> On Thu, Sep 13, 2018 at 04:16:21PM +0300, Ville Syrjala wrote:
> >>> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >>>
> >>> We wish to control certain driver_features flags on a per-device basis
> >>> while still sharing a single drm_driver instance across all the
> >>> devices. To that end introduce device.driver_features. By default
> >>> it will be set to ~0 to not impose any limits beyond
> >>> driver.driver_features. Drivers can then clear specific flags
> >>> in the per-device bitmask to limit the capabilities of the device.
> >>>
> >>> An alternative approach would be to copy the driver_features from
> >>> the driver into the device in drm_dev_init(), however that would
> >>> require verifying that no driver is currently changing
> >>> driver.driver_features after drm_dev_init(). Hence the ~0 apporach
> >>> was easier.
> >>>
> >>> Ideally we'd also make drm_driver const but there is plenty of code
> >>> left that wants to mutate it (eg. various vfunc assignments). We'll
> >>> need to fix all that up before we can make it const.
> >>>
> >>> And while at it fix up the type of the feature flag passed to
> >>> drm_core_check_feature().
> >>>
> >>> v2: Streamline the && vs. & (Chris)
> >>>     s/int/u32/ in drm_core_check_feature() args
> >>>
> >>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> >>> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >>
> >> git grep DRIVER_ATOMIC -- drivers/gpu/drm/nouveau has a 2nd supporting
> >> case for this. Exactly same problem as we have here. Would be good to also
> >> convert that one, for a bit of OCD.
> > 
> > Thanks for pointing it out. I'll cook it up and send separately after
> > this lands.
> 
> I don't suppose you'd like to do amdgpu as well, while you're at it? :)

Sure. I'll take a gander at it as well.

-- 
Ville Syrjälä
Intel
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