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

Akash Asthana <akashast@xxxxxxxxxxxxxx> · Fri, 20 Mar 2020 16:05:06 +0530

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@xxxxxxxxxxxxxx>
---
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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