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

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Sun, Mar 17, 2024 at 10:41:23PM +0100, Hans de Goede wrote:
> 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.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.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.

Yep. When I reviewed the original submission I was got puzzled with
the CLK APIs. Now I might remember that ->set_rate() can't be called
on prepared/enabled clocks and it's possible the same limitation
is applied to ->round_rate().

I also tried to find documentation about the requirements for those
APIs, but failed (maybe was not pursuing enough, dunno). If you happen
to know the one, can you point on it?

-- 
With Best Regards,
Andy Shevchenko