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Date: Tue, 10 Apr 2012 22:34:03 +0100 From: Chris Wilson <chris@...is-wilson.co.uk> To: Daniel Vetter <daniel@...ll.ch>, Daniel Kurtz <djkurtz@...omium.org> Cc: Keith Packard <keithp@...thp.com>, David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, Benson Leung <bleung@...omium.org>, Yufeng Shen <miletus@...omium.org> Subject: Re: [PATCH 4/8 v7] drm/i915/intel_i2c: use WAIT cycle, not STOP On Tue, 10 Apr 2012 17:03:04 +0200, Daniel Vetter <daniel@...ll.ch> wrote: > On Tue, Apr 10, 2012 at 06:56:15PM +0800, Daniel Kurtz wrote: > > On Tue, Apr 10, 2012 at 6:41 PM, Daniel Vetter <daniel@...ll.ch> wrote: > > > On Tue, Apr 10, 2012 at 12:37:46PM +0200, Daniel Vetter wrote: > > >> On Fri, Mar 30, 2012 at 07:46:39PM +0800, Daniel Kurtz wrote: > > >> > The i915 is only able to generate a STOP cycle (i.e. finalize an i2c > > >> > transaction) during a DATA or WAIT phase. In other words, the > > >> > controller rejects a STOP requested as part of the first transaction in a > > >> > sequence. > > >> > > > >> > Thus, for the first transaction we must always use a WAIT cycle, detect > > >> > when the device has finished (and is in a WAIT phase), and then either > > >> > start the next transaction, or, if there are no more transactions, > > >> > generate a STOP cycle. > > >> > > > >> > Note: Theoretically, the last transaction of a multi-transaction sequence > > >> > could initiate a STOP cycle. However, this slight optimization is left > > >> > for another patch. We return -ETIMEDOUT if the hardware doesn't > > >> > deactivate after the STOP cycle. > > >> > > > >> > Signed-off-by: Daniel Kurtz <djkurtz@...omium.org> > > >> > > >> I've re-read gmbus register spec and STOP seems to be allowed even in the > > >> first cycle. Does this patch solve an issue for you? If not, I prefer we > > >> just drop it. > > > > STOP does not work in the first cycle, hence the patch. > > Ok, I've picked this patch up and extended the comment a bit to that > effect. Just to avoid anyone else trying to 'fix' things because bspec > sounds like it should work. > > I've also picked up the other patches safe for the last one, thanks a lot > for digging through the gmbus code and fixing it all up. > > Now can I volunteer you for a (hopefully) last set of gmbus patches? > Afaics there are a few small things left to fix: > - zero-length reads can blow up the kernel, like zero-length writes could. > See: https://bugs.freedesktop.org/show_bug.cgi?id=48269 > - Chris Wilson suggested on irc that we should wait for HW_READY even for > zero-length writes (and also reads), currently we don't. > - atm the debug output is too noisy. I think we can leave the fallback to > gpio bitbanging at info (or maybe error) level, but all the other > messages should be tuned down to DRM_DEBUG_KMS - these can easily be hit > when userspace tries to probe the i2c with nothing connected or if the > driver code tries to do the same. See: > https://bugs.freedesktop.org/show_bug.cgi?id=48248 > > Chris, anything you want to add to the wishlist? The last major item on the wishlist is solving how to drive the SDVO i2c over gmbus. I think it is just a matter of massaging in the channel switch as msg[0]. -Chris -- Chris Wilson, Intel Open Source Technology Centre -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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