Re: [PATCH 0/3] RFC: Add a drm_aux-dev module.

From: Jani Nikula <jani.nikula@linux.intel.com>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Daniel Vetter" <daniel@ffwll.ch>
Cc: daniel.vetter@ffwll.ch, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 0/3] RFC: Add a drm_aux-dev module.
Date: Thu, 17 Sep 2015 10:01:38 +0300	[thread overview]
Message-ID: <87r3lxttpp.fsf@intel.com> (raw)
In-Reply-To: <20150916204721.GL26517@intel.com>

On Wed, 16 Sep 2015, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Wed, Sep 16, 2015 at 01:09:54PM -0700, Daniel Vetter wrote:
>> On Tue, Sep 15, 2015 at 10:03:09AM -0700, Rafael Antognolli wrote:
>> > On Tue, Sep 15, 2015 at 07:46:55PM +0300, Ville Syrjälä wrote:
>> > > On Tue, Sep 15, 2015 at 07:41:06PM +0300, Ville Syrjälä wrote:
>> > > > On Tue, Sep 15, 2015 at 09:34:15AM -0700, Rafael Antognolli wrote:
>> > > > > On Tue, Sep 15, 2015 at 10:35:19AM +0300, Ville Syrjälä wrote:
>> > > > > > On Mon, Sep 14, 2015 at 04:12:29PM -0700, Rafael Antognolli wrote:
>> > > > > > > This is a tentative implementation of a module that allows reading/writing
>> > > > > > > arbitrary dpcd registers, following the suggestion from Daniel Vetter. It
>> > > > > > > assumes the drm aux helpers were used by the driver.
>> > > > > > > 
>> > > > > > > I tried to follow the i2c-dev implementation as close as possible, but the only
>> > > > > > > operations that are provided on the dev node are two different ioctl's, one for
>> > > > > > > reading a register and another one for writing it.
>> > > > > > 
>> > > > > > Why would you use ioctls instead of normal read/write syscalls?
>> > > > > > 
>> > > > > 
>> > > > > For writing, that should work fine, I can easily change that if you
>> > > > > prefer.
>> > > > > 
>> > > > > For reading, one has to first tell which register address is going to be
>> > > > > read.
>> > > > 
>> > > > seek()
>> > > 
>> > > Sorry typo. Make that lseek(). 
>> > > 
>> > Oh, nice, I'll update the patch with this and remove the notifier stuff,
>> > thanks!
>> 
>> Well there's also other modes like i2c over aux, and that would be easier
>> to support with an ioctl in a uniform way. So not sure how much value
>> there is in reusing read/write for i2c ...
>
> We already have i2c-dev for i2c. So not sure what you're after here.

Yeah, definitely don't reinvent the wheel for this.

BR,
Jani.

>
> i2c is a bit of a mess on the protocol level. Lots of devices do
> interesting things with it, so it can't really make do with just
> read/write/lseek. Apart from i2c-over-aux, the rest is all about
> DPCD access, and for that read/write/lseek is all you ever need.
>
> -- 
> Ville Syrjälä
> Intel OTC
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Jani Nikula, Intel Open Source Technology Center
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