[PATCH master] ARM: omap: fix NS16550 UART setup in omap_debug_ll_init

[PATCH master] ARM: omap: fix NS16550 UART setup in omap_debug_ll_init

[Ahmad Fatoum]

The NS16550 on the OMAP SoCs has a special mode register that contains a
disable bit. In order to use the peripheral, this bit needs to be
cleared.

We do that in ns16550_omap_init_port() and used to it for the DEBUG_LL
case in omap_uart_lowlevel_init().

Commit 89094b2a299b ("ARM: omap: Use ns16550 debug_ll helper") removed
this mode register write for the DEBUG_LL case, thereby rendering
DEBUG_LL on the BeagleBone Black non-functional.

Add back the missing register write to fix this.

This has not been tested on AM6xx, but the barebox proper driver also
writes a zero (after writing 0x80), so it's assumed that this write
would be a no-op there, because either the POR default or a previous
boot stage does already configure the peripheral this way.

Fixes: 89094b2a299b ("ARM: omap: Use ns16550 debug_ll helper")
Reported-by: Konstantin Kletschke <konstantin.kletschke@inside-m2m.de>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 include/debug_ll/ns16550.h   | 1 +
 include/mach/omap/debug_ll.h | 1 +
 2 files changed, 2 insertions(+)

diff --git a/include/debug_ll/ns16550.h b/include/debug_ll/ns16550.h
index 2bad7a43ca91..64cb9cd102df 100644
--- a/include/debug_ll/ns16550.h
+++ b/include/debug_ll/ns16550.h
@@ -19,6 +19,7 @@
 #define NS16550_LCR	0x3
 #define NS16550_MCR	0x4
 #define NS16550_LSR	0x5
+#define NS16550_MDR	0x8	/* TI OMAP Mode register */
 
 #define NS16550_LCR_VAL		0x3 /* 8 data, 1 stop, no parity */
 #define NS16550_MCR_VAL		0x3 /* RTS/DTR */
diff --git a/include/mach/omap/debug_ll.h b/include/mach/omap/debug_ll.h
index b0650abf2daa..a95c1bf140ac 100644
--- a/include/mach/omap/debug_ll.h
+++ b/include/mach/omap/debug_ll.h
@@ -57,6 +57,7 @@ static inline void omap_debug_ll_init(void)
 
 	divisor = debug_ll_ns16550_calc_divisor(48000000);
 	debug_ll_ns16550_init(base, divisor);
+	debug_ll_write_reg(base, NS16550_MDR, 0);
 }
 
 static inline void PUTC_LL(int c)
-- 
2.39.5

Re: [PATCH master] ARM: omap: fix NS16550 UART setup in omap_debug_ll_init

[Konstantin Kletschke]

Tested-by: Konstantin Kletschke <konstantin.kletschke@inside-m2m.de> # BBB

Re: [PATCH master] ARM: omap: fix NS16550 UART setup in omap_debug_ll_init

[Sascha Hauer]

On Tue, 03 Dec 2024 21:24:47 +0100, Ahmad Fatoum wrote:
> The NS16550 on the OMAP SoCs has a special mode register that contains a
> disable bit. In order to use the peripheral, this bit needs to be
> cleared.
> 
> We do that in ns16550_omap_init_port() and used to it for the DEBUG_LL
> case in omap_uart_lowlevel_init().
> 
> [...]

Applied, thanks!

[1/1] ARM: omap: fix NS16550 UART setup in omap_debug_ll_init
      https://git.pengutronix.de/cgit/barebox/commit/?id=f8debca379c0 (link may not be stable)

Best regards,
-- 
Sascha Hauer <s.hauer@pengutronix.de>