Am Freitag, den 31.07.2015, 18:35 +0900 schrieb jiwang: > Hi Dirk and Lucas > > On 07/31/2015 05:13 PM, Dirk Behme wrote: > > On 31.07.2015 09:40, Lucas Stach wrote: > >> Hi Dirk, > >> > >> Am Freitag, den 31.07.2015, 08:40 +0200 schrieb Dirk Behme: > >>> On 19.05.2015 14:16, Fabio Estevam wrote: > >>>> Hi Philipp, > >>>> > >>>> On Tue, May 19, 2015 at 5:54 AM, Philipp Zabel > >>>> <p.zabel@xxxxxxxxxxxxxx> wrote: > >>>>> The driver configures the IDLE condition to interrupt the SDMA engine. > >>>>> Since the SDMA UART ROM script doesn't clear the IDLE bit itself, this > >>>>> caused repeated 1-byte DMA transfers, regardless of available data > >>>>> in the > >>>>> RX FIFO. Also, when returning due to the IDLE condition, the UART ROM > >>>>> script already increased its counter, causing residue to be off by > >>>>> one. > >>>>> > >>>>> This patch clears the IDLE condition to avoid repeated 1-byte DMA > >>>>> transfers > >>>>> and decreases count by when the DMA transfer was aborted due to the > >>>>> IDLE > >>>>> condition, fixing serial transfers using DMA on i.MX6Q. > >>>>> > >>>>> Reported-by: Peter Seiderer <ps.report@xxxxxxx> > >>>>> Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> > >>>> > >>>> Thanks for the fix. Tested on a imx6sl-warp, where I could not use DMA > >>>> to access a Bluetooth device using the ROM SDMA firmware. > >>>> > >>>> Tested-by: Fabio Estevam <fabio.estevam@xxxxxxxxxxxxx> > >>>> > >>>> Could you please also Cc stable? > >>> > >>> > >>> Just fyi: We got this patch via -stable, and found that it results in > >>> issues for us. So we had to revert it in our local tree. > >>> > >>> We are using the DMA with baud rates > 2Mbit/s. Having a quick look at > >>> the registers in the ARM Reference Manual, USR2_IDLE seems to be a flag > >>> that is set when the RX line has been idle for at least a defined amount > >>> of time. > >>> > >>> For us this commit is dangerous because it fails to check whether the > >>> IDLE CONDITION feature is being used. We don't use the RX IDLE CONDITION > >>> feature, therefore it is likely to cause the last received character to > >>> be discarded causing corruption of data. > >>> > >>> From your description it's not clear to me why this commit is causing > >> issues for you. The idle condition signaling is automatically enabled > >> when using DMA. > >> > >> The idle signaling should only ever fire if the line has been idle for > >> 32byte durations. The aging timer, that expires after data is sitting in > >> the FIFO for 8 byte durations, should have flushed out all data at this > >> point. > >> > >> Do you use a RAM SDMA firmware or do you rely on the internal one. > > > > To my understanding we are using a RAM SDMA firmware. If I read the > > various mailing list thread correctly, the difference between the RAM > > SDMA firmware and the internal one was already often a root cause for > > different behavior. > > I did some simply tests, > found RAM firmware clears IDLE bit while ROM script doesn't, > so I assume there also could be some difference on how counter is > handled in RAM firmware and ROM script. > > Based on our test, I think this patch only works for ROM script. So someone didn't understand that you just can not alter the behavior of the SDMA script between versions without seriously complicating matters for the software. However I found some clues in the documentation that suggest that the current driver code doesn't handle things correctly. I'll spin a patch for that, hopefully this will allow to also fix things for the RAM firmware. Regards, Lucas -- Pengutronix e.K. | Lucas Stach | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
