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

[Rafael Antognolli <rafael.antognolli@intel.com>]

On Wed, Sep 16, 2015 at 11:47:21PM +0300, Ville Syrjälä 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.
> 
> 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.

I just noticed that I forgot to cc you guys, but yesterday I sent an
updated version of the patch set to this list:

http://lists.freedesktop.org/archives/dri-devel/2015-September/090366.html

I also don't have a strong opinion about ioctl vs read/write/lseek, but
at least my second implementation did get a little cleaner.

Thanks,
Rafael
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