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Date: Tue, 31 Mar 2020 15:58:29 +0000
From: Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>,
Kazuhiro Fujita <kazuhiro.fujita.jg@...esas.com>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.com>,
"open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
Prabhakar <prabhakar.csengg@...il.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Hao Bui <hao.bui.yg@...esas.com>,
KAZUMI HARADA <kazumi.harada.rh@...esas.com>,
Sasha Levin <sashal@...nel.org>,
Chris Brandt <Chris.Brandt@...esas.com>
Subject: RE: [PATCH] serial: sh-sci: Make sure status register SCxSR is read
in correct sequence
Hi Geert,
Thank you for the review.
> -----Original Message-----
> From: Geert Uytterhoeven <geert@...ux-m68k.org>
> Sent: 31 March 2020 16:18
> To: Kazuhiro Fujita <kazuhiro.fujita.jg@...esas.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>; Jiri Slaby <jslaby@...e.com>; open list:SERIAL DRIVERS <linux-
> serial@...r.kernel.org>; Linux-Renesas <linux-renesas-soc@...r.kernel.org>; Prabhakar <prabhakar.csengg@...il.com>; Linux Kernel
> Mailing List <linux-kernel@...r.kernel.org>; Hao Bui <hao.bui.yg@...esas.com>; KAZUMI HARADA <kazumi.harada.rh@...esas.com>;
> Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>; Sasha Levin <sashal@...nel.org>; Chris Brandt
> <Chris.Brandt@...esas.com>
> Subject: Re: [PATCH] serial: sh-sci: Make sure status register SCxSR is read in correct sequence
>
> Hi Fujita-san,
>
> CC -stable, +sasha, +seebe
>
> On Fri, Mar 27, 2020 at 7:17 PM Kazuhiro Fujita
> <kazuhiro.fujita.jg@...esas.com> wrote:
> > For SCIF and HSCIF interfaces the SCxSR register holds the status of
> > data that is to be read next from SCxRDR register, But where as for
> > SCIFA and SCIFB interfaces SCxSR register holds status of data that is
> > previously read from SCxRDR register.
> >
> > This patch makes sure the status register is read depending on the port
> > types so that errors are caught accordingly.
> >
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Kazuhiro Fujita <kazuhiro.fujita.jg@...esas.com>
> > Signed-off-by: Hao Bui <hao.bui.yg@...esas.com>
> > Signed-off-by: KAZUMI HARADA <kazumi.harada.rh@...esas.com>
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
>
> Thanks for your patch!
>
> > --- a/drivers/tty/serial/sh-sci.c
> > +++ b/drivers/tty/serial/sh-sci.c
> > @@ -870,9 +870,16 @@ static void sci_receive_chars(struct uart_port *port)
> > tty_insert_flip_char(tport, c, TTY_NORMAL);
> > } else {
> > for (i = 0; i < count; i++) {
> > - char c = serial_port_in(port, SCxRDR);
> > -
> > - status = serial_port_in(port, SCxSR);
> > + char c;
> > +
> > + if (port->type == PORT_SCIF ||
> > + port->type == PORT_HSCIF) {
> > + status = serial_port_in(port, SCxSR);
> > + c = serial_port_in(port, SCxRDR);
> > + } else {
> > + c = serial_port_in(port, SCxRDR);
> > + status = serial_port_in(port, SCxSR);
> > + }
> > if (uart_handle_sysrq_char(port, c)) {
> > count--; i--;
> > continue;
>
> I can confirm that the documentation for the Serial Status Register on
> 1. (H)SCIF on R-Car Gen1/2/3 says the framing/error flag applies to
> the data that is "to be read next" from the FIFO., and that the
> "Sample Flowchart for Serial Reception (2)" confirms this,
> 2. SCIF[AB] on R-Car Gen2, SH-Mobile AG5, R-Mobile A1 and APE6 says
> the framing/error flag applies to the receive data that is "read"
> from the FIFO, and that the "Example of Flow for Serial Reception
> (2)" confirms this,
> 3. SCIF on RZ/A1H says something similar as for (H)SCIF above, using
> slightly different wording, also confirmed by the "Sample Flowchart
> for Receiving Serial Data (2)".
>
> However, the documentation for "SCIFA" on RZ/A2 (for which we use
> PORT_SCIF, not PORT_SCIFA, in the driver) has conflicting information:
> 1. Section 17.2.7 "Serial Status Register (FSR)" says:
> - A receive framing/parity error occurred in the "next receive
> data read" from the FIFO,
> - Indicates whether there is a framing/parity error in the data
> "read" from the FIFO.
> 2. Figure 17.8 "Sample Flowchart for Receiving Serial Data in
> Asynchronous Mode (2)".
> - Whether a framing error or parity error has occurred in the
> received data that is "read" from the FIFO.
>
> So while the change looks OK for most Renesas ARM SoCs, the situation
> for RZ/A2 is unclear.
> Note that the above does not take into account variants used on SuperH
> SoCs.
>
I'll dig out some documentation wrt RZ/A2 & SuperH. Also H8300 needs to be considered. By any chance do you have RZ/A2 to test 😊.
> Nevertheless, this patch will need some testing on various hardware.
> Do you have a test case to verify the broken/fixed behavior?
>
Agreed, its been tested on RZ/G2x & RZ/G1x by doing a loopback test, configure one interface as CS8 mode(8-bits data, No parity) and other as CS7 mode (7-bits data, 1-bit Parity) and parity errors should be detected.
Cheers,
--Prabhakar
> Thanks!
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds
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