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 tree. > > > > > > [rebased to i2c-current/i2c-next/mainline-3.10-rc1] > > > > > > Signed-off-by: Christian Ruppert <christian.ruppert@xxxxxxxxxx> > > > Signed-off-by: Pierrick Hascoet <pierrick.hascoet@xxxxxxxxxx> > > > > Hmm, I really have problems adding a generic property. I need to better > > understand why this is needed? What is the usecase? Can't a safe value > > be calculated depending on the bus-speed? Is there a public datasheet > > available somewhere? > > 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 and > 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 > > 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 parameter > to an appropriate value. The value seems to be different for different > PCBs. Yeah, we see the same problem. Our platform guys have solved this so that 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 i2c > bus master hardware. If you don't want to add a generic property, would > you accept the patch with the property renamed to dwi2c,sda-hold-time? > > Greetings, > Christian > > > -- > Christian Ruppert , <christian.ruppert@xxxxxxxxxx> > /| > Tel: +41/(0)22 816 19-42 //| 3, Chemin du Pré-Fleuri > _// | bilis Systems CH-1228 Plan-les-Ouates -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
