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serial: sh: Fix error handling

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The current SCIF error handling is broken for the RZ/G2L. After a break
condition has been triggered, the current code is unable to clear the
error and serial port output never resumes.

The RZ/G2L datasheet says that most error conditions are cleared by
resetting the relevant error bits in the FSR & LSR registers to zero.
To clear framing errors on SCIF ports, the invalid data also needs to be
read out of the receive FIFO.

After reviewing datasheets for RZ/G2{H,M,N,E}, R-Car Gen4, R-Car Gen3
and even SH7751 SoCs, it's clear that this is the way to clear errors
for all of these SoCs.

While we're here, annotate the handle_error() function with a couple of
comments as the reads and writes themselves don't immediately make it
clear what we're doing.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Tested-by: Chris Paterson <chris.paterson2@renesas.com> # HiHope RZ/G2M board
Tested-by: Marek Vasut <marek.vasut+renesas@mailbox.org> # R-Car H3 Salvator-XS
This commit is contained in:
Paul Barker 2023-10-19 15:30:43 +01:00 committed by Marek Vasut
parent e463222cce
commit 0f924d88fa
1 changed files with 14 additions and 2 deletions
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16
drivers/serial/serial_sh.c
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@ -79,10 +79,22 @@ 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));
/*
* Most errors are cleared by resetting the relevant error bits to zero
* in the FSR & LSR registers. For each register, a read followed by a
* write is needed according to the relevant datasheets.
*/
unsigned short status = sci_in(port, SCxSR);
sci_out(port, SCxSR, status & ~SCxSR_ERRORS(port));
sci_in(port, SCLSR);
sci_out(port, SCLSR, 0x00);
/*
* To clear framing errors, we also need to read and discard a
* character.
*/
if ((port->type != PORT_SCI) && (status & SCIF_FER))
sci_in(port, SCxRDR);
}
static int serial_raw_putc(struct uart_port *port, const char c)