[PATCH] serial: imx: Only enable UART DMA on i.MX6Q and i.MX53

[clemens.gruber@pqgruber.com (Clemens Gruber)]

On Sun, Feb 05, 2017 at 02:36:10PM -0200, Fabio Estevam wrote:
> On Sun, Feb 5, 2017 at 12:56 PM, Fabio Estevam <fabio.estevam@nxp.com> wrote:
> > [Sorry, for the top-posting]
> >
> >
> > imx6sx uart should be of a IMX6Q_UART instead.
> >
> >
> > Does this patch fix the issue?
> 
> It seems this dts change will not fix the problem.
> 
> > From: Kai Ruhnau <kai.ruhnau@target-sg.com>
> >
> > In 1c06bde6 with the introduction of DMA support for the i.MX53 platform,
> > DMA was enabled for all platforms instead. On an i.MX6SX (which is a
> > IMX21_UART), this breaks gpsd talking to an UART module with
> >
> >  imx-uart 21f4000.serial: DMA transaction error.
> >
> > This patch makes sure, UART DMA is only activated for i.MX53 and i.MX6Q.
> >
> > Signed-off-by: Kai Ruhnau <kai.ruhnau@target-sg.com>
> > Reviewed-by: Marek Vasut <marex@denx.de>
> > Fixes: 1c06bde643d0 ("Allowing UART DMA to be configured on i.MX53")
> > Cc: <stable@vger.kernel.org> # 4.9+
> > Cc: Fabio Estevam <fabio.estevam@nxp.com>
> > Cc: Martyn Welch <martyn.welch@collabora.co.uk>
> > Cc: Shawn Guo <shawnguo@kernel.org>
> > ---
> >  drivers/tty/serial/imx.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> > index a70356d..8e2b5f2 100644
> > --- a/drivers/tty/serial/imx.c
> > +++ b/drivers/tty/serial/imx.c
> > @@ -1269,7 +1269,8 @@ static int imx_startup(struct uart_port *port)
> >          writel(temp & ~UCR4_DREN, sport->port.membase + UCR4);
> >
> >          /* Can we enable the DMA support? */
> > -       if (!uart_console(port) && !sport->dma_is_inited)
> > +       if ((is_imx6q_uart(sport)  || is_imx53_uart(sport)) &&
> > +           !uart_console(port) && !sport->dma_is_inited)
> >                  imx_uart_dma_init(sport);
> 
> Looks like imx serial DMA is broken in 4.9.

There are probably two separate problems:

A)
I also observed the DMA transaction error message when I used the ROM
SDMA scripts. Seems to affect single- and multi-core systems and is
fixed by: github.com/Freescale/linux-fslc/commit/a2ec8df37f5d (?)
This is also not RS-485 specific, but affects RS-232 too.

B)
The RS-485 DMA problem I reported, which only affects multi-core
systems.
RS-232 DMA is not affected.

> 
> There is also this report from Clemens: https://lkml.org/lkml/2017/1/4/579
> 
> Could anyone run a git bisect?

I reverted tty/serial/imx.c to the first implementation of RS-485,
namely to commit 17b8f2a3fdca ("serial: imx: add support for half duplex
rs485"). Also had to add "fsl," in front of uart-has-rts-cts in the DT.
But it does not work either (same behavior). Looks like RS-485 DMA never
worked on SMP systems..?

It's still a mistery to me what is causing the xmit->tail index to walk
over the xmit->head index, leading to the rest of the whole
UART_XMIT_SIZE buffer to be sent out. But it must be connected to the
transmit-complete interrupt, because if I disable it, this does not
happen.

Thanks,
Clemens