[PATCH] serial: 8250_dw: Revert: Do not reclock if already at correct rate

Hans de Goede
2024-03-17T21:41:56Z

Commit e5d6bd25f93d ("serial: 8250_dw: Do not reclock if already at
correct rate") breaks the dw UARTs on Intel Bay Trail (BYT) and
Cherry Trail (CHT) SoCs.

Before this change the RTL8732BS Bluetooth HCI which is found
connected over the dw UART on both BYT and CHT boards works properly:

Bluetooth: hci0: RTL: examining hci_ver=06 hci_rev=000b lmp_ver=06 lmp_subver=8723
Bluetooth: hci0: RTL: rom_version status=0 version=1
Bluetooth: hci0: RTL: loading rtl_bt/rtl8723bs_fw.bin
Bluetooth: hci0: RTL: loading rtl_bt/rtl8723bs_config-OBDA8723.bin
Bluetooth: hci0: RTL: cfg_sz 64, total sz 24508
Bluetooth: hci0: RTL: fw version 0x365d462e

where as after this change probing it fails:

Bluetooth: hci0: RTL: examining hci_ver=06 hci_rev=000b lmp_ver=06 lmp_subver=8723
Bluetooth: hci0: RTL: rom_version status=0 version=1
Bluetooth: hci0: RTL: loading rtl_bt/rtl8723bs_fw.bin
Bluetooth: hci0: RTL: loading rtl_bt/rtl8723bs_config-OBDA8723.bin
Bluetooth: hci0: RTL: cfg_sz 64, total sz 24508
Bluetooth: hci0: command 0xfc20 tx timeout
Bluetooth: hci0: RTL: download fw command failed (-110)

Revert the changes to fix this regression.

Fixes: e5d6bd25f93d ("serial: 8250_dw: Do not reclock if already at correct rate")
Cc: stable@vger.kernel.org
Cc: Peter Collingbourne <pcc@google.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Note it is not entirely clear to me why this commit is causing
this issue. Maybe probe() needs to explicitly set the clk rate
which it just got (that feels like a clk driver issue) or maybe
the issue is that unless setup before hand by firmware /
the bootloader serial8250_update_uartclk() needs to be called
at least once to setup things ? Note that probe() does not call
serial8250_update_uartclk(), this is only called from the
dw8250_clk_notifier_cb()

This requires more debugging which is why I'm proposing
a straight revert to fix the regression ASAP and then this
can be investigated further.
---
drivers/tty/serial/8250/8250_dw.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index c1d43f040c43..2d1f350a4bea 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -357,9 +357,9 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
long rate;
int ret;

+ clk_disable_unprepare(d->clk);
rate = clk_round_rate(d->clk, newrate);
- if (rate > 0 && p->uartclk != rate) {
- clk_disable_unprepare(d->clk);
+ if (rate > 0) {
/*
* Note that any clock-notifer worker will block in
* serial8250_update_uartclk() until we are done.
@@ -367,8 +367,8 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
ret = clk_set_rate(d->clk, newrate);
if (!ret)
p->uartclk = rate;
- clk_prepare_enable(d->clk);
}
+ clk_prepare_enable(d->clk);

dw8250_do_set_termios(p, termios, old);
}
--
2.44.0