[RFC v2 03/11] tty: serial: qcom_geni_serial: Use OPP API to set clk/perf state

[Rajendra Nayak]

On 8/12/2020 7:03 AM, John Stultz wrote:
> On Tue, Aug 11, 2020 at 4:11 PM John Stultz <john.stultz at linaro.org> wrote:
>>
>> On Wed, Mar 20, 2019 at 2:49 AM Rajendra Nayak <rnayak at codeaurora.org> wrote:
>>>
>>> geni serial needs to express a perforamnce state requirement on CX
>>> depending on the frequency of the clock rates. Use OPP table from
>>> DT to register with OPP framework and use dev_pm_opp_set_rate() to
>>> set the clk/perf state.
>>>
>>> Signed-off-by: Rajendra Nayak <rnayak at codeaurora.org>
>>> Signed-off-by: Stephen Boyd <swboyd at chromium.org>
>>> ---
>>>   drivers/tty/serial/qcom_geni_serial.c | 15 +++++++++++++--
>>>   1 file changed, 13 insertions(+), 2 deletions(-)
>>>
>>
>> Hey,
>>    I just wanted to follow up on this patch, as I've bisected it
>> (a5819b548af0) down as having broken qca bluetooth on the Dragonboard
>> 845c.
>>
>> I haven't yet had time to debug it yet, but wanted to raise the issue
>> in case anyone else has seen similar trouble.
> 
> So I dug in a bit further, and this chunk seems to be causing the issue:
>> @@ -961,7 +963,7 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport,
>>                  goto out_restart_rx;
>>
>>          uport->uartclk = clk_rate;
>> -       clk_set_rate(port->se.clk, clk_rate);
>> +       dev_pm_opp_set_rate(port->dev, clk_rate);
>>          ser_clk_cfg = SER_CLK_EN;
>>          ser_clk_cfg |= clk_div << CLK_DIV_SHFT;
>>
> 
> 
> With that applied, I see the following errors in dmesg and bluetooth
> fails to function:
> [    4.763467] qcom_geni_serial 898000.serial: dev_pm_opp_set_rate:
> failed to find OPP for freq 102400000 (-34)
> [    4.773493] qcom_geni_serial 898000.serial: dev_pm_opp_set_rate:
> failed to find OPP for freq 102400000 (-34)
> 
> With just that chunk reverted on linus/HEAD, bluetooth seems to work ok.

This seems like the same issue that was also reported on venus [1] because the
clock frequency tables apparently don;t exactly match the achievable clock
frequencies (which we also used to construct the OPP tables)

Can you try updating the OPP table for QUP to have 102400000 instead of the
current 100000000 and see if that fixes it?

[1] https://lkml.org/lkml/2020/7/27/507

> 
> thanks
> -john
> 

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