Re: [PATCH V4 4/9] soc: qcom-geni-se: Add interconnect support to fix earlycon crash

[Akash Asthana <akashast@xxxxxxxxxxxxxx>]

Hi Matthias,

On 4/16/2020 6:01 AM, Matthias Kaehlcke wrote:
> Hi Akash,
>
> On Wed, Apr 15, 2020 at 03:53:13PM +0530, Akash Asthana wrote:
> > QUP core clock is shared among all the SE drivers present on particular
> > QUP wrapper, the system will reset(unclocked access) if earlycon used after
> > QUP core clock is put to 0 from other SE drivers before real console comes
> > up.
> >
> > As earlycon can't vote for it's QUP core need, to fix this add ICC
> > support to common/QUP wrapper driver and put vote for QUP core from
> > probe on behalf of earlycon and remove vote during earlycon exit call.
> >
> > Signed-off-by: Akash Asthana <akashast@xxxxxxxxxxxxxx>
> > Reported-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> > ---
> > Change in V3:
> >   - Add geni_remove_earlycon_icc_vote API that will be used by earlycon
> >     exit function to remove ICC vote for earlyconsole.
> >   - Remove suspend/resume hook for geni-se driver as we are no longer
> >     removing earlyconsole ICC vote from system suspend, we are removing
> >     from earlycon exit.
> >
> > Change in V4:
> >   - As per Matthias comment make 'earlycon_wrapper' as static structure.
> >
> >   drivers/soc/qcom/qcom-geni-se.c       | 50 +++++++++++++++++++++++++++++++++++
> >   drivers/tty/serial/qcom_geni_serial.c |  7 +++++
> >   include/linux/qcom-geni-se.h          |  2 ++
> >   3 files changed, 59 insertions(+)
> >
> > diff --git a/drivers/soc/qcom/qcom-geni-se.c b/drivers/soc/qcom/qcom-geni-se.c
> > index 1527bc4..727ad2e 100644
> > --- a/drivers/soc/qcom/qcom-geni-se.c
> > +++ b/drivers/soc/qcom/qcom-geni-se.c
> > @@ -90,8 +90,11 @@ struct geni_wrapper {
> >   	struct device *dev;
> >   	void __iomem *base;
> >   	struct clk_bulk_data ahb_clks[NUM_AHB_CLKS];
> > +	struct geni_icc_path to_core;
> >   };
> >   
> > +static struct geni_wrapper *earlycon_wrapper;
> > +
> >   #define QUP_HW_VER_REG			0x4
> >   
> >   /* Common SE registers */
> > @@ -781,6 +784,26 @@ int geni_icc_vote_off(struct geni_se *se)
> >   }
> >   EXPORT_SYMBOL(geni_icc_vote_off);
> >   
> > +void geni_remove_earlycon_icc_vote(void)
> > +{
> > +	struct geni_wrapper *wrapper = earlycon_wrapper;
> > +	struct device_node *parent = of_get_next_parent(wrapper->dev->of_node);
> > +	struct device_node *child;
> > +
> > +	for_each_child_of_node(parent, child) {
> > +		if (of_device_is_compatible(child, "qcom,geni-se-qup")) {
> > +			wrapper = platform_get_drvdata(of_find_device_by_node(
> > +					child));
> > +			icc_put(wrapper->to_core.path);
> > +			wrapper->to_core.path = NULL;
> > +		}
> > +	}
> > +	of_node_put(parent);
> > +
> > +	earlycon_wrapper = NULL;
> > +}
> > +EXPORT_SYMBOL(geni_remove_earlycon_icc_vote);
> > +
> >   static int geni_se_probe(struct platform_device *pdev)
> >   {
> >   	struct device *dev = &pdev->dev;
> > @@ -808,6 +831,33 @@ static int geni_se_probe(struct platform_device *pdev)
> >   		}
> >   	}
> >   
> > +#ifdef CONFIG_SERIAL_EARLYCON
> > +	wrapper->to_core.path = devm_of_icc_get(dev, "qup-core");
> > +	if (IS_ERR(wrapper->to_core.path))
> > +		return PTR_ERR(wrapper->to_core.path);
> > +	/*
> > +	 * Put minmal BW request on core clocks on behalf of early console.
> > +	 * The vote will be removed earlycon exit function.
> > +	 *
> > +	 * Note: We are putting vote on each QUP wrapper instead only to which
> > +	 * earlycon is connected because QUP core clock of different wrapper
> > +	 * share same voltage domain. If core1 is put to 0, then core2 will
> > +	 * also run at 0, if not voted. Default ICC vote will be removed ASA
> > +	 * we touch any of the core clock.
> > +	 * core1 = core2 = max(core1, core2)
> > +	 */
> > +	ret = icc_set_bw(wrapper->to_core.path, GENI_DEFAULT_BW, 0);
> > +	if (ret) {
> > +		dev_err(&pdev->dev, "%s: ICC BW voting failed for core\n",
> > +			__func__);
> > +		return ret;
> > +	}
> > +
> > +	if (of_get_compatible_child(pdev->dev.of_node, "qcom,geni-debug-uart"))
> > +		earlycon_wrapper = wrapper;
> > +	of_node_put(pdev->dev.of_node);
> > +#endif
> > +
> >   	dev_set_drvdata(dev, wrapper);
> >   	dev_dbg(dev, "GENI SE Driver probed\n");
> >   	return devm_of_platform_populate(dev);
> > diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> > index 6119090..8c5d97c 100644
> > --- a/drivers/tty/serial/qcom_geni_serial.c
> > +++ b/drivers/tty/serial/qcom_geni_serial.c
> > @@ -1090,6 +1090,12 @@ static void qcom_geni_serial_earlycon_write(struct console *con,
> >   	__qcom_geni_serial_console_write(&dev->port, s, n);
> >   }
> >   
> > +static int qcom_geni_serial_earlycon_exit(struct console *con)
> > +{
> > +	geni_remove_earlycon_icc_vote();
> > +	return 0;
> > +}
> > +
> >   static int __init qcom_geni_serial_earlycon_setup(struct earlycon_device *dev,
> >   								const char *opt)
> >   {
> > @@ -1135,6 +1141,7 @@ static int __init qcom_geni_serial_earlycon_setup(struct earlycon_device *dev,
> >   	writel(stop_bit_len, uport->membase + SE_UART_TX_STOP_BIT_LEN);
> >   
> >   	dev->con->write = qcom_geni_serial_earlycon_write;
> > +	dev->con->exit = qcom_geni_serial_earlycon_exit;
> The idea of using the exit handler of the early console to remove the
> votes seemed appealing at first, however it has a drawback: the bandwidth
> requests in geni_se_probe() are always made when CONFIG_SERIAL_EARLYCON=y,
> also when the system doesn't actually use an early console. On such a
> system the votes would never be removed.
>
> A possible alternative could seem to remove the vote at the end of
> qcom_geni_serial_probe() of the 'normal' console, but it has a similar
> problem: the system could not even have a normal console. One could
> possibly argue that CONFIG_SERIAL_QCOM_GENI_CONSOLE shouldn't be set
> on such a system, however it could be enabled to have a console for
> development, and in production the same kernel config is used, but
> with the console disabled through the device tree.
>
> I don't really have a good idea at this point, maybe we just need
> something as ugly as a delayed work to remove the votes. Other
> suggestions are welcome :)

I think we can do something like below. Before voting we are checking 
whether earlyconsole ("qcom_geni") exits or not.  The name is fixed from 
earlycon declaration file@drivers/tty/serial/qcom_geni_serial.c

OF_EARLYCON_DECLARE(qcom_geni, "qcom,geni-debug-uart",
                                qcom_geni_serial_earlycon_setup);

====================================================================================

@@ -809,6 +809,8 @@ static int geni_se_probe(struct platform_device *pdev)
        struct device *dev = &pdev->dev;
        struct resource *res;
        struct geni_wrapper *wrapper;
+       struct console *bcon = NULL;
+       int earlycon_present = 0;
        int ret;

        wrapper = devm_kzalloc(dev, sizeof(*wrapper), GFP_KERNEL);
@@ -832,6 +834,15 @@ static int geni_se_probe(struct platform_device *pdev)
        }

 #ifdef CONFIG_SERIAL_EARLYCON
+       if (console_drivers)
+               for_each_console(bcon)
+                       if (!strcmp(bcon->name, "qcom_geni")) {
+                               earlycon_present = 1;
+                               break;
+                       }
+       if(!earlycon_present)
+               goto exit;
+
        wrapper->to_core.path = devm_of_icc_get(dev, "qup-core");
        if (IS_ERR(wrapper->to_core.path))
                return PTR_ERR(wrapper->to_core.path);
@@ -858,6 +869,7 @@ static int geni_se_probe(struct platform_device *pdev)
        of_node_put(pdev->dev.of_node);
 #endif

+exit:
        dev_set_drvdata(dev, wrapper);
        dev_dbg(dev, "GENI SE Driver probed\n");
        return devm_of_platform_populate(dev);

======================================================================================

Regards,

Akash

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