Re: [PATCH REBASE] i2c-designware: make SDA hold time configurable
From: Mika Westerberg
Date: Mon Jun 17 2013 - 04:19:40 EST
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
Sorry for the delay, I was on vacation.
I'm not aware of any publicly available datasheets for this block,
> 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.
> 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
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?
> Christian Ruppert , <christian.ruppert@xxxxxxxxxx>
> Tel: +41/(0)22 816 19-42 //| 3, Chemin du Pré-Fleuri
> _// | bilis Systems CH-1228 Plan-les-Ouates
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