Re: [PATCH RFC] drm/atomic: Fall back to legacy call back in *_connector_dpms()

From: Jyri Sarha <jsarha@ti.com>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Tomi Valkeinen" <tomi.valkeinen@ti.com>
Cc: rmk+kernel@arm.linux.org.uk, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH RFC] drm/atomic: Fall back to legacy call back in *_connector_dpms()
Date: Mon, 15 Feb 2016 11:47:46 +0200	[thread overview]
Message-ID: <56C19EC2.6070905@ti.com> (raw)
In-Reply-To: <20160212171543.GQ23290@intel.com>

On 02/12/16 19:15, Ville Syrjälä wrote:
> On Fri, Feb 12, 2016 at 07:08:46PM +0200, Tomi Valkeinen wrote:
>> On 12/02/16 17:34, Daniel Vetter wrote:
>>> On Fri, Feb 12, 2016 at 05:17:19PM +0200, Jyri Sarha wrote:
>>>> Fall back to legacy drm_helper_connector_dpms() call back in
>>>> drm_atomic_helper_connector_dpms() if DRIVER_ATOMIC feature is not
>>>> present.
>>>>
>>>> Calling drm_atomic_helper_connector_dpms() from non atomic driver
>>>> causes undefined behavior. This is a problem with componentized
>>>> encoder/connector drivers that may be bound to both atomic and
>>>> non atomic drivers.drm-next-tilcdc-fixes
>>>>
>>>> Signed-off-by: Jyri Sarha <jsarha@ti.com>
>>>> ---
>>>> This is just an alternative to this:
>>>> https://lists.freedesktop.org/archives/dri-devel/2016-January/098867.html
>>>
>>> I like the linked patch much better, since non-atomic really should die.
>>> Inflicting non-atomic on atomic helpers is bad imo, so nack from me on
>>> this patch here.
>>
>> I mostly agree, but we are in a transition period from non-atomic to
>> atomic. When all drivers have been converted to atomic, it should be
>> easy to grep for code using DRIVER_ATOMIC (or similar), and remove all
>> the non-atomic support code.
>>
>> In my opinion it should be considered case by case if the
>> non-atomic/atomic compat code should be added to the generic functions
>> or to all the drivers using that functionality.
>>
>> In this case, if it only affects tda998x (but does it?), perhaps the
>> patch in the link is better.
>
> Maybe we need a hybrid helper that just calls the atomic
> or non-atomic helper approppriately.
>

Would it actually be better if the legacy callback would automatically 
call atomic version if the driver has DRIVER_ATOMIC set?

I do not have any strong opinions on this, just as long as one of the 
patches gets merged. With quick grepping I can see that there are 
several DRM component drivers, but I have no idea if anything else but 
the tda998x is being used by more than one DRM master driver.

Best regards,
Jyri
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