Am Donnerstag, den 20.09.2018, 08:39 +0000 schrieb Robin Gong: > > -----Original Message----- > > From: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> > > Sent: 2018年9月20日 15:55 > > To: Robin Gong <yibin.gong@xxxxxxx> > > Cc: jslaby@xxxxxxxx; Andy Duan <fugang.duan@xxxxxxx>; > > linux-serial@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; dl- > > linux-imx > > <linux-imx@xxxxxxx>; kernel@xxxxxxxxxxxxxx > > Subject: Re: [PATCH v1] tty: serial: imx: enable IDDMAEN for the > > last tail data > > > > Hello, > > > > On Thu, Sep 20, 2018 at 11:26:00PM +0800, Robin Gong wrote: > > > enable IDDMAEN in UCR4 to let sdma script has the chance to > > > detect the > > > idle status and transfer the last tail data with the interrupt > > > notifying uart driver.Otherwise, the last dma done interrupt of > > > the > > > tail data in rxfifo whose size is less than watermark may never > > > be > > > received by uart driver. > > > > Is this a theoretic issue? Or does it fix a real problem? > > > > If the former I'd say UCR1_ATDMAEN being set should prevent this > > stall. > > It's a real fix, you will see 'timeout We read 0 byte' with the > attached stress test > running on i.mx7d or i.mx6 if no this patch applied. > ' while [ 1 ]; do /unit_tests/UART/mxc_uart_stress_test.out > /dev/ttymxc5 2000000 D L 100 100 L; done &' > Please make sure dma enabled on ttymxcX for your test, and sdma > firmware setup in your rootfs > /lib/firmware/imx/sdma/sdma-imx6q.bin or /lib/firmware/imx/sdma/sdma- > imx7d.bin. > You can get sdma firmware from below: > https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux- > firmware.git/tree/imx/sdma Please see commit 905c0decad28402aa166975023fb88c8f62f93c8 on why using the idle detect together with with SDMA is wrong. We don't want to re- introduce the broken behavior. Regards, Lucas
