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From: Matthias Kaehlcke <mka-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
To: Akash Asthana <akashast-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
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	evgreen-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org
Subject: Re: [PATCH V2 4/8] tty: serial: qcom_geni_serial: Add interconnect support
Date: Thu, 19 Mar 2020 13:42:48 -0700
Message-ID: <20200319204248.GA204494@google.com> (raw)
In-Reply-To: <e95bd6e0-d1fd-9d13-47df-f7d08b443e37-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>

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-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.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.

> 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

  parent reply index

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-13 13:12 [PATCH V2 0/8] Add interconnect support to QSPI and QUP drivers Akash Asthana
     [not found] ` <1584105134-13583-1-git-send-email-akashast-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
2020-03-13 13:12   ` [PATCH V2 1/8] interconnect: Add devm_of_icc_get() as exported API for users Akash Asthana
2020-03-13 16:26     ` Matthias Kaehlcke
2020-03-27 23:02     ` Bjorn Andersson
2020-03-13 13:12   ` [PATCH V2 4/8] tty: serial: qcom_geni_serial: Add interconnect support Akash Asthana
     [not found]     ` <1584105134-13583-5-git-send-email-akashast-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
2020-03-13 21:28       ` Matthias Kaehlcke
     [not found]         ` <20200313212833.GK144492-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2020-03-17 11:48           ` Akash Asthana
2020-03-17 19:08             ` Matthias Kaehlcke
2020-03-18 12:23               ` Akash Asthana
     [not found]                 ` <e95bd6e0-d1fd-9d13-47df-f7d08b443e37-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
2020-03-19 20:42                   ` Matthias Kaehlcke [this message]
     [not found]                     ` <20200319204248.GA204494-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2020-03-20 10:35                       ` Akash Asthana
2020-03-13 13:12   ` [PATCH V2 5/8] i2c: i2c-qcom-geni: " Akash Asthana
2020-03-14  0:17     ` Matthias Kaehlcke
2020-03-17 11:51       ` Akash Asthana
2020-03-13 13:12   ` [PATCH V2 6/8] spi: spi-geni-qcom: " Akash Asthana
     [not found]     ` <1584105134-13583-7-git-send-email-akashast-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
2020-03-13 13:16       ` Mark Brown
2020-03-17  9:35         ` Akash Asthana
     [not found]           ` <aa197568-3bac-6962-d39d-3261f68c0514-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
2020-03-17 13:06             ` Mark Brown
2020-03-20 13:52               ` Akash Asthana
2020-03-14  0:41     ` Matthias Kaehlcke
     [not found]       ` <20200314004106.GM144492-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2020-03-17 12:11         ` Akash Asthana
2020-03-13 13:12 ` [PATCH V2 2/8] soc: qcom: geni: Support for ICC voting Akash Asthana
2020-03-13 16:42   ` Matthias Kaehlcke
     [not found]     ` <20200313164207.GH144492-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2020-03-17  9:58       ` Akash Asthana
2020-03-17 19:06   ` Evan Green
     [not found]     ` <74851dda-296d-cdc5-2449-b9ec59bbc057@codeaurora.org>
2020-03-20 16:45       ` Evan Green
2020-03-27  5:33         ` Akash Asthana
2020-03-13 13:12 ` [PATCH V2 3/8] soc: qcom-geni-se: Add interconnect support to fix earlycon crash Akash Asthana
2020-03-13 20:44   ` Matthias Kaehlcke
     [not found]     ` <20200313204441.GJ144492-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2020-03-17 10:57       ` Akash Asthana
     [not found]         ` <1f86fdf0-df7c-4e4a-d4d8-8b0162e52cb4-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
2020-03-17 18:29           ` Matthias Kaehlcke
2020-03-18  8:54             ` Akash Asthana
2020-03-19 19:43               ` Matthias Kaehlcke
     [not found]                 ` <20200319194332.GA60149-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2020-03-20 10:22                   ` Akash Asthana
2020-03-20 16:30                     ` Evan Green
2020-03-27  5:04                       ` Akash Asthana
2020-03-27 23:23                       ` Bjorn Andersson
2020-03-31 10:55                         ` Akash Asthana
2020-03-17 19:08           ` Evan Green
2020-03-17 19:46             ` Doug Anderson
     [not found]             ` <CAE=gft5GcOeQ5kh1bGen_P0J98g2XaAJ7NrDsxkirDoLtL4GWg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-03-18 10:57               ` Akash Asthana
2020-03-18 16:22                 ` Evan Green
2020-03-13 13:12 ` [PATCH V2 7/8] spi: spi-qcom-qspi: Add interconnect support Akash Asthana
2020-03-14  0:58   ` Matthias Kaehlcke
     [not found]     ` <20200314005817.GN144492-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2020-03-17 12:13       ` Akash Asthana
2020-03-17 19:08         ` Evan Green
2020-03-18 13:48           ` Akash Asthana
     [not found]             ` <e2ee1a60-a379-5c78-355a-64aad451a944-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
2020-03-18 16:30               ` Evan Green
2020-03-20  5:35                 ` Akash Asthana
2020-03-13 13:12 ` [PATCH V2 8/8] arm64: dts: sc7180: Add interconnect for QUP and QSPI Akash Asthana

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