[PATCH 10/16] serial: sh: Add RZ/G2L SCIF support

[Paul Barker]

On Wed, Oct 04, 2023 at 02:26:49PM +0200, Marek Vasut wrote:
> On 10/4/23 10:48, Paul Barker wrote:
> > On 03/10/2023 14:23, Marek Vasut wrote:
> > > On 9/20/23 14:42, Paul Barker wrote:
> > > > Extend the existing driver to support the SCIF serial ports on the
> > > > Renesas RZ/G2L (R9A07G044) SoC. This also requires us to ensure that the
> > > > relevant reset signal is de-asserted before we try to talk to the SCIF
> > > > module.
> > > > 
> > > > Signed-off-by: Paul Barker <paul.barker.ct at bp.renesas.com>
> > > > Reviewed-by: Biju Das <biju.das.jz at bp.renesas.com>
> > > > Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj at bp.renesas.com>
> > > > ---
> > > >    arch/arm/mach-rmobile/Kconfig |  1 +
> > > >    drivers/serial/serial_sh.c    | 32 ++++++++++++++++++++++++++++++--
> > > >    drivers/serial/serial_sh.h    | 19 ++++++++++++++++++-
> > > >    3 files changed, 49 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/arch/arm/mach-rmobile/Kconfig b/arch/arm/mach-rmobile/Kconfig
> > > > index 973e84fcf7ba..0ab22356aee5 100644
> > > > --- a/arch/arm/mach-rmobile/Kconfig
> > > > +++ b/arch/arm/mach-rmobile/Kconfig
> > > > @@ -77,6 +77,7 @@ config RZG2L
> > > >    	imply RENESAS_SDHI
> > > >    	imply CLK_RZG2L
> > > >    	imply PINCTRL_RZG2L
> > > > +	imply SCIF_CONSOLE
> > > >    	help
> > > >    	  Enable support for the Renesas RZ/G2L family of SoCs, including the
> > > >    	  the RZ/G2L itself (based on the R9A07G044 SoC).
> > > > diff --git a/drivers/serial/serial_sh.c b/drivers/serial/serial_sh.c
> > > > index 5e543dbf3d58..a2e9a57137a6 100644
> > > > --- a/drivers/serial/serial_sh.c
> > > > +++ b/drivers/serial/serial_sh.c
> > > > @@ -17,6 +17,8 @@
> > > >    #include <linux/compiler.h>
> > > >    #include <dm/platform_data/serial_sh.h>
> > > >    #include <linux/delay.h>
> > > > +#include <dm/device_compat.h>
> > > > +#include <reset.h>
> > > >    #include "serial_sh.h"
> > > >    DECLARE_GLOBAL_DATA_PTR;
> > > > @@ -79,8 +81,16 @@ sh_serial_setbrg_generic(struct uart_port *port, int clk, int baudrate)
> > > >    static void handle_error(struct uart_port *port)
> > > >    {
> > > > -	sci_in(port, SCxSR);
> > > > -	sci_out(port, SCxSR, SCxSR_ERROR_CLEAR(port));
> > > > +	/* The RZ/G2L datasheet says that error conditions are cleared by
> > > > +	 * resetting the error bits in the FSR register to zero.
> > > 
> > > Can you be more specific here ?
> > > 
> > > It doesn't seem Linux sh-sci.c driver does anything special for G2L, so
> > > is this special case really needed ?
> > 
> > On page 1268 of the datasheet (R01UH0914EJ0130 Rev.1.30):
> > 
> > "DR is cleared to 0 when DR = 1 is read and then 0 is written to the DR
> > flag."
> > 
> > On page 1270:
> > 
> > "[Clearing condition]
> > ● When 0 is written to ER after it has been read as 1"
> > 
> > So zeros must be written to clear these errors, not ones.
> > 
> > We have an open task to investigate the issue in the Linux driver and
> > fix it.
> 
> Is the G2L UART broken in Linux ?

Likely yes, but we need to reproduce the issue.

> Does it misbehave in U-Boot ?

Yes, before I changed this, if a framing error occurred it could never
be cleared and the serial port stopped sending/receiving data.

The framing error was triggered by accident by unnecessarily re-doing
pinmuxing for the serial port after TrustedFirmware had already set it
up correctly. Since SCIF0 is wired to an FTDI USB/serial adaptor chip on
the SMARC carrier board, it seems very difficult to trigger a framing
error in any other way, the FTDI chip is too well behaved.

Thanks,
Paul
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