Re: [PATCH V2 4/8] tty: serial: qcom_geni_serial: Add interconnect support

[Akash Asthana <akashast@codeaurora.org>]

Hi Matthias,

On 3/20/2020 2:12 AM, Matthias Kaehlcke wrote:
> On Wed, Mar 18, 2020 at 05:53:22PM +0530, Akash Asthana wrote:
>> Hi Matthias,
>>
>> On 3/18/2020 12:38 AM, Matthias Kaehlcke wrote:
>>> On Tue, Mar 17, 2020 at 05:18:34PM +0530, Akash Asthana wrote:
>>>> Hi Matthias,
>>>>
>>>> On 3/14/2020 2:58 AM, Matthias Kaehlcke wrote:
>>>>> Hi Akash,
>>>>>
>>>>> On Fri, Mar 13, 2020 at 06:42:10PM +0530, Akash Asthana wrote:
>>>>>> Get the interconnect paths for Uart based Serial Engine device
>>>>>> and vote according to the baud rate requirement of the driver.
>>>>>>
>>>>>> Signed-off-by: Akash Asthana <akashast@codeaurora.org>
>>>>>> ---
>>>>>> Changes in V2:
>>>>>>     - As per Bjorn's comment, removed se == NULL check from geni_serial_icc_get
>>>>>>     - As per Bjorn's comment, removed code to set se->icc_path* to NULL in failure
>>>>>>     - As per Bjorn's comment, introduced and using devm_of_icc_get API for getting
>>>>>>       path handle
>>>>>>     - As per Matthias comment, added error handling for icc_set_bw call
>>>>>>
>>>>>>     drivers/tty/serial/qcom_geni_serial.c | 69 +++++++++++++++++++++++++++++++++--
>>>>>>     1 file changed, 65 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
>>>>>> index 272bae0..c8ad7e9 100644
>>>>>> --- a/drivers/tty/serial/qcom_geni_serial.c
>>>>>> +++ b/drivers/tty/serial/qcom_geni_serial.c
>>>>>>
>>>>>> ...
>>>>>>
>>>>>>     static int qcom_geni_serial_request_port(struct uart_port *uport)
>>>>>>     {
>>>>>>     	struct platform_device *pdev = to_platform_device(uport->dev);
>>>>>> @@ -962,6 +975,7 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport,
>>>>>>     	struct qcom_geni_serial_port *port = to_dev_port(uport, uport);
>>>>>>     	unsigned long clk_rate;
>>>>>>     	u32 ver, sampling_rate;
>>>>>> +	int ret;
>>>>>>     	qcom_geni_serial_stop_rx(uport);
>>>>>>     	/* baud rate */
>>>>>> @@ -983,6 +997,18 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport,
>>>>>>     	ser_clk_cfg = SER_CLK_EN;
>>>>>>     	ser_clk_cfg |= clk_div << CLK_DIV_SHFT;
>>>>>> +	/*
>>>>>> +	 * Put BW vote only on CPU path as driver supports FIFO mode only.
>>>>>> +	 * Assume peak_bw as twice of avg_bw.
>>>>>> +	 */
>>>>>> +	port->se.avg_bw_cpu = Bps_to_icc(baud);
>>>>>> +	port->se.peak_bw_cpu = Bps_to_icc(2 * baud);
>>>>>> +	ret = icc_set_bw(port->se.icc_path_cpu_to_geni, port->se.avg_bw_cpu,
>>>>>> +			port->se.peak_bw_cpu);
>>>>>> +	if (ret)
>>>>>> +		dev_err(uport->dev, "%s: ICC BW voting failed for cpu\n",
>>>>>> +			__func__);
>>>>> Should this return an error? The port might not operate properly if the ICC
>>>>> bandwidth couldn't be configured
>>>> This is void function we can't return error from here. I guess it would be
>>>> somewhat okay if BW voting failed for CPU path but clk_set_rate failure is
>>>> more serious which is called from this function, I don't think it can be
>>>> move to somewhere else.
>>> ok, I missed that _set_termios() is void.
>>>
>>>>>>     static const struct uart_ops qcom_geni_console_pops = {
>>>>>> @@ -1308,6 +1358,17 @@ static int qcom_geni_serial_probe(struct platform_device *pdev)
>>>>>>     	port->rx_fifo_depth = DEF_FIFO_DEPTH_WORDS;
>>>>>>     	port->tx_fifo_width = DEF_FIFO_WIDTH_BITS;
>>>>>> +	ret = geni_serial_icc_get(&port->se);
>>>>>> +	if (ret)
>>>>>> +		return ret;
>>>>>> +	/* Set the bus quota to a reasonable value */
>>>>>> +	port->se.avg_bw_core = console ? Bps_to_icc(1000) :
>>>>>> +		Bps_to_icc(CORE_2X_50_MHZ);
>>>>> Why different settings for console vs. non-console?
>>>> QUP FW runs on core clock. To support higher throughput we want FW to run at
>>>> higher speed.
>>>>
>>>> Since Console operate at 115200bps and BT operate at 3.2Mbps baud. We are
>>>> voting higher on core for BT usecase.
>>>>
>>>> These value are recommended from HW team.
>>> IIUC none of the values you mention are set in stone. 115200bps seems to be a
>>> 'standard' value for the serial console, but it could be a different baudrate.
>>> I guess you are referring to Qualcomm Bluetooth controllers, which are only one
>>> of many things that could be connected to the port. And what happens when a
>>> QCA BT controller is connected to a non-geni/QCA port, which doesn't know about
>>> its 'requirements'? The answer is that both the BT controller and the serial
>>> console configure the baudrate they need, hence using different values in
>>> _probe() is pointless.
>> Are you refering other UART drivers(not based on geni HW) as non-geni/QCA
>> port?
>>
>> We are not scaling core BW request based on real time need like we are doing
>> for other paths(CPU/DDR) instead we are using some fail proof value because,
>> FW runs on core clock and core behaves a bit different than other NOCs.
>>
>> We don't have any functional relation which maps actual throughput
>> requirement to core frequency need. In the past we faced few latency issues
>> because of core slowness (Although it was running much higher than actual
>> throughput requirement). To avoid such scenario we are using recommend value
>> from HW team. These fix value can support SE drivers operating at their max
>> possible speed(4Mbps in case of non-console).
> ok, I missed that the core clocks aren't scaled based on the configured
> baudrate. Apparently experience shows that it is not practical due to the
> latency issues you mention.
Yeah That is correct.
>> I agree that 115200bps seems to be a 'standard' value for the serial
>> console, but it could be a different baudrate.
>>
>> We are voting 1000 in case of console because it  has low power mode
>> use-case in android, where voting CORE_2X_50_MHZ can be reported as a power
>> issue.
>>
>> Actually we wanted to vote 960 for console but that is not possible with
>> current ICC design where the minimum value is 1000bps.  So any way core is
>> running at 50 MHz as 1000 crosses the threshold for 19.2 MHz (960)
>>
>> only with console.
> Thanks for the clarification. So if a board wanted to use a higher baudrate
> for the console it (currently) shouldn't be a problem. While it would be nice
> to have uniform settings for all UARTs it's also not a big deal to have two
> values, just wanted to make sure it's needed

Okay, but I would like to keep as it is with above mentioned reason.


Thanks,

Akash

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