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

[Matthias Kaehlcke <mka@xxxxxxxxxxxx>]

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 :)