Am Mittwoch, dem 02.10.2024 um 16:56 +0200 schrieb Stefan Eichenberger: > On Wed, Oct 02, 2024 at 04:40:32PM +0200, Lucas Stach wrote: > > Am Mittwoch, dem 02.10.2024 um 13:19 +0200 schrieb Stefan Eichenberger: > > > From: Stefan Eichenberger <stefan.eichenberger@xxxxxxxxxxx> > > > > > > According to the i.MX8M Mini reference manual chapter "16.1.4.2 > > > Generation of Start" it is only necessary to poll for bus busy and > > > arbitration lost in multi master mode. This helps to avoid rescheduling > > > while the i2c bus is busy and avoids SMBus devices to timeout. > > > > > This is a backward incompatible change, as far as I can see. Until now > > the driver would properly handle a multi-mastered bus, without any > > specific configuration. Now it requires the new multi-master DT > > property to be set, which isn't even documented in the binding to be > > understood by this driver. > > > > Are you sure that every single instance of a i.MX i2c bus is only > > single mastered? > > > > If this is a worthwhile performance improvement I guess you need to > > flip the logic around by adding a new single-master DT property (or > > something along those lines), which should go through proper DT binding > > review. You can then use this property for boards/busses to opt into > > skipping the arbitration lost check. > > According to the discussion here the property documentation should not > be added: > https://lore.kernel.org/linux-i2c/2bbddaxyjkxfmlgmq3yqcbzo7dsb2pq5bvdatk2y4ig4iintkt@35btqkdv7sy3/ > Ah, I wasn't aware of that. > However, the point regarding single-master and multi-master is correct. > We also discussed this internally and assumed the single-master use case > is more likely to be the default and that this patch series would fix > issues for other devices out there. > I agree that the vast majority of busses is single master only and I can see why you did it this way. However, I still think it's a risky change, as some boards/DTs may rely on the fact that the driver implicitly handled multi-master until now and we can't retroactively change DTs in the wild. I just looked up the dtschema for i2c-controller and there is a "single-master" property defined already. I think it would be good if you used this instead to have boards opt in to this optimization. Regards, Lucas > However, your point is valid and if > preferred I can change it to single-master with the next version. > > Francesco Dolcini <francesco.dolcini@xxxxxxxxxxx> I think you once had a > discussion regarding multi master mode for i2c on i.MX devices? Maybe > you can remember the details? > > Regards, > Stefan
