On Thu, Aug 23, 2012 at 07:06:53AM -0700, Shirish S wrote: > Hello Daniel, > > On Thu, Aug 23, 2012 at 1:54 AM, Daniel Vetter <daniel@xxxxxxxx> wrote: > > > On Wed, Aug 22, 2012 at 10:52:26AM +0300, Ville Syrjälä wrote: > > > On Tue, Aug 21, 2012 at 04:28:20PM -0700, Shirish S wrote: > > > > On Tue, Aug 21, 2012 at 7:56 AM, Ville Syrjälä < > > > > ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > On Tue, Aug 21, 2012 at 06:55:53AM -0700, Shirish S wrote: > > > > Here are my earlier comments on Jean's patch: > > > > > > > http://lists.freedesktop.org/archives/dri-devel/2012-February/019069.html > > > > > > > > > > > > > > If i am not wrong am doing exactly what you have said in you comments. > > > > > > > > This seems a bit wrong to me. The spec says that the ack for the > > > > segment address is "don't care", but for the segment pointer the ack is > > > > required (when segment != 0). > > > > The variable segFlags is "dont care for block 0 and 1 wheras". > > > > > > > > With I2C_M_IGNORE_NAK we would in fact end up reading segment 0 from a > > > > non E-DDC display, if we try to read segment != 0 from it. Of course > > > > we shouldn't do that unless the display lied to us about what extension > > > > blocks it provides. > > > > > > > > So I'm not sure if it would be better to trust that the display never > > > > lies about the extension blocks, or if we should just assume all E-DDC > > > > displays ack both segment addr and pointer. The no-ack feature seems > > > > to there for backwards compatibility, for cases where the host always > > > > sends the segment addr/pointer even when reading segment 0 (which your > > > > code doesn't do). > > > > > > > > To handle it exactly as the spec says, I2C_M_IGNORE_NAK should be split > > > > into two flags (one for addr, other for data). > > > > > > > > Hence i have split the i2c_msg into 3, segment pointer,offset(addr) > > > > and data pointer. > > > > > > I was referring to the addr and data phases of the segment pointer. > > > According to the spec the ack for the addr is always optional. But I > > > suppose no sane device would nak the addr, while acking the data. > > > > We've seen those. Really. > > > > Which is why the current i915 gmbus driver has a hack to never return a > > NaK on the first i2c transfer. I guess we should fix this by properly > > supporting the INGNORE_NAK field in our gmbus driver, and setting that on > > the addr transfer field, too. > > > > Thanks for the comment, so are you ok with the current logic? > > > > I concure with Ville that sending the segment i2c message only when we > > actually need it, and not unconditionally. DDC is way to broken and > > claiming that the spec says otherwise doesn't fix all the existing bad hw. > > > > Agreed, so do you want me to post another patch, in which i add a function > only > if the number of blocks is more than 2? > Also i had some mistake in the patch set 1, hence i updated it. I think adding the IGNORE_NAK on the addr i2c transaction would help unconditionally - like I've said we've seen monitors that suggest that this is required. And yeah, I think we should send the E-DDC segment number only if the basic edid block indicates that more than 2 blocks are availble (and again with IGNORE_NAK, just for paranoia's sake). > Kindly have a look! Will do. Yours, Daniel -- Daniel Vetter Mail: daniel@xxxxxxxx Mobile: +41 (0)79 365 57 48 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
