On Tue, Aug 04, 2020 at 10:35:12AM +0800, Shengjiu Wang wrote: > On Tue, Aug 4, 2020 at 10:11 AM Nicolin Chen <nicoleotsuka@xxxxxxxxx> wrote: > > > > On Tue, Aug 04, 2020 at 09:39:44AM +0800, Shengjiu Wang wrote: > > > On Tue, Aug 4, 2020 at 5:57 AM Nicolin Chen <nicoleotsuka@xxxxxxxxx> wrote: > > > > > > > > On Mon, Aug 03, 2020 at 04:04:23PM +0800, Shengjiu Wang wrote: > > > > > > > > > > > clock generation. The TCSR.TE is no need to enabled when only RX > > > > > > > is enabled. > > > > > > > > > > > > You are correct if there's only RX running without TX joining. > > > > > > However, that's something we can't guarantee. Then we'd enable > > > > > > TE after RE is enabled, which is against what RM recommends: > > > > > > > > > > > > # From 54.3.3.1 Synchronous mode in IMX6SXRM > > > > > > # If the receiver bit clock and frame sync are to be used by > > > > > > # both the transmitter and receiver, it is recommended that > > > > > > # the receiver is the last enabled and the first disabled. > > > > > > > > > > > > I remember I did this "ugly" design by strictly following what > > > > > > RM says. If hardware team has updated the RM or removed this > > > > > > limitation, please quote in the commit logs. > > > > > > > > > > There is no change in RM and same recommandation. > > > > > > > > > > My change does not violate the RM. The direction which generates > > > > > the clock is still last enabled. > > > > > > > > Using Tx syncing with Rx clock for example, > > > > T1: arecord (non-stop) => set RE > > > > T2: aplay => set TE then RE (but RE is already set at T1) > > > > > > > > Anything that I am missing? > > > > > > This is a good example. > > > We have used this change locally for a long time, so I think it is > > > safe to do this change, a little different with the recommandation. > > > > Any reason for we have to go against the recommendation? > > Previous code will enable TE and RE together even for asynchronous > mode. > And for recommendation, previous code just consider the RX sync with > TX, but still violates the recommendation for TX sync with RX case. > So at least this new change is some kind of improvement. Okay. Let's change it then. Please make sure to update/remove those old comments in the trigger(). And it's probably better to mention that what we do now is a bit different from RM: /* * Enable the opposite direction for synchronous mode * 1. Tx sync with Rx: only set RE for Rx; set TE & RE for Tx * 2. Rx sync with Tx: only set TE for Tx; set RE & TE for Rx * * RM recommends to enable RE after TE for case 1 and to enable * TE after RE for case 2, but we here may not always guarantee * that happens: "arecord 1.wav; aplay 2.wav" in case 1 enables * TE after RE, which is against what RM recommends but should * be safe to do, judging by years of testing results. */ Btw, do we need similar change for TRIGGER_STOP?
