From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mika Westerberg Subject: Re: [PATCH REBASE] i2c-designware: make SDA hold time configurable Date: Mon, 17 Jun 2013 11:23:31 +0300 Message-ID: <20130617082331.GG11878@intel.com> References: <20130514110745.GA10906@intel.com> <1368536642-7158-1-git-send-email-christian.ruppert@abilis.com> <20130610152954.GE2987@katana> <20130612144743.GB8102@ab42.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <20130612144743.GB8102@ab42.lan> Sender: linux-doc-owner@vger.kernel.org To: Christian Ruppert Cc: Wolfram Sang , linux-i2c@vger.kernel.org, "Ben Dooks (embedded platforms)" , Grant Likely , Rob Herring , Rob Landley , devicetree-discuss@lists.ozlabs.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Vineet Gupta , Pierrick Hascoet List-Id: linux-i2c@vger.kernel.org On Wed, Jun 12, 2013 at 04:47:45PM +0200, Christian Ruppert wrote: > On Mon, Jun 10, 2013 at 05:29:55PM +0200, Wolfram Sang wrote: > > On Tue, May 14, 2013 at 03:04:02PM +0200, Christian Ruppert wrote: > > > This patch makes the SDA hold time configurable through device tr= ee. > > >=20 > > > [rebased to i2c-current/i2c-next/mainline-3.10-rc1] > > >=20 > > > Signed-off-by: Christian Ruppert > > > Signed-off-by: Pierrick Hascoet > >=20 > > Hmm, I really have problems adding a generic property. I need to be= tter > > understand why this is needed? What is the usecase? Can't a safe va= lue > > be calculated depending on the bus-speed? Is there a public datashe= et > > available somewhere? >=20 > I checked with our PCB/Applications team and the data sheets for the > peripherals in question (DVB demodulator front ends) are under NDA. > Mika, you seem to be interested in this patch as well. Do you know of > any publicly available data sheets for hardware requiring this > adjustment? Sorry for the delay, I was on vacation. I'm not aware of any publicly available datasheets for this block, unfortunately. > In the case of the Designware block, the parameter both changes SDA a= nd > START hold times, however, and you'll find lots of data sheets for > hardware with START hold time requirements on the net, e.g. > http://ww1.microchip.com/downloads/en/DeviceDoc/21805B.pdf >=20 > The empirical solution in the function i2c_dw_scl_hcnt does not seem = to > work in all cases: Our lab guys confirmed that we have several PCB > designs which do not work without adjusting the sda-hold-time paramet= er > to an appropriate value. The value seems to be different for differen= t > PCBs. Yeah, we see the same problem. Our platform guys have solved this so th= at they made the SDA hold time available from ACPI to the device driver. > I suspect that this kind of configurability is not the same for all i= 2c > bus master hardware. If you don't want to add a generic property, wou= ld > you accept the patch with the property renamed to dwi2c,sda-hold-time= ? >=20 > Greetings, > Christian >=20 >=20 > --=20 > Christian Ruppert , > /| > Tel: +41/(0)22 816 19-42 //| 3, Chemin du Pr=E9= -Fleuri > _// | bilis Systems CH-1228 Plan-les-O= uates