Re: [PATCH V3 3/8] soc: qcom-geni-se: Add interconnect support to fix earlycon crash

[Matthias Kaehlcke <mka@chromium.org>]

Hi Akash,

On Tue, Mar 31, 2020 at 04:39:31PM +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@codeaurora.org>
> Reported-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> Change is 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.
> 
>  drivers/soc/qcom/qcom-geni-se.c       | 51 +++++++++++++++++++++++++++++++++++
>  drivers/tty/serial/qcom_geni_serial.c |  7 +++++
>  include/linux/qcom-geni-se.h          |  2 ++
>  3 files changed, 60 insertions(+)
> 
> diff --git a/drivers/soc/qcom/qcom-geni-se.c b/drivers/soc/qcom/qcom-geni-se.c
> index 9344c14..d30c282 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;
>  };
>  
> +struct geni_wrapper *earlycon_wrapper;

should be static

> +
>  #define QUP_HW_VER_REG			0x4
>  
>  /* Common SE registers */
> @@ -818,6 +821,26 @@ 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);

I didn't know that consoles have an exit handler, this is way nicer than
the miscellaneous triggers we discussed earlier :)

> +
>  static int geni_se_probe(struct platform_device *pdev)
>  {
>  	struct device *dev = &pdev->dev;
> @@ -845,6 +868,34 @@ 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)
> +	 */

I don't really understand this part. According to the comment if we vote
(let's say) for core2 but not for core1 then:

core1: 0
core2: GENI_DEFAULT_BW

core1 = core2 = max(core1, core2)
  or
core1 = core2 = max(0, GENI_DEFAULT_BW)

hence

core1 = core2 = GENI_DEFAULT_BW

What am I missing, why is it necessary to vote for both/all?