Subject: Re: [PATCH 3/3] remoteproc/k3-dsp: Add support for L2RAM loading on C66x DSPs

From: Mathieu Poirier <[email-masked]>
Date: Tue, 28 Apr 2020 13:58:55 -0600

On Wed, Mar 25, 2020 at 03:18:39PM -0500, Suman Anna wrote:
> The resets for the DSP processors on K3 SoCs are managed through the
> Power and Sleep Controller (PSC) module. Each DSP typically has two
> resets - a global module reset for powering on the device, and a local
> reset that affects only the CPU while allowing access to the other
> sub-modules within the DSP processor sub-systems.
> 
> The C66x DSPs have two levels of internal RAMs that can be used to
> boot from, and the firmware loading into these RAMs require the
> local reset to be asserted with the device powered on/enabled using
> the module reset. Enhance the K3 DSP remoteproc driver to add support
> for loading into the internal RAMs. The local reset is deasserted on
> SoC power-on-reset, so logic has to be added in probe in remoteproc
> mode to balance the remoteproc state-machine.
> 
> Note that the local resets are a no-op on C71x cores, and the hardware
> does not supporting loading into its internal RAMs.
> 
> Signed-off-by: Suman Anna <[email-masked]>
> ---
>  drivers/remoteproc/ti_k3_dsp_remoteproc.c | 82 +++++++++++++++++++++++
>  1 file changed, 82 insertions(+)
> 
> diff --git a/drivers/remoteproc/ti_k3_dsp_remoteproc.c b/drivers/remoteproc/ti_k3_dsp_remoteproc.c
> index fd0d84f46f90..7b712ef74611 100644
> --- a/drivers/remoteproc/ti_k3_dsp_remoteproc.c
> +++ b/drivers/remoteproc/ti_k3_dsp_remoteproc.c
> @@ -175,6 +175,9 @@ static int k3_dsp_rproc_reset(struct k3_dsp_rproc *kproc)
>  		return ret;
>  	}
>  
> +	if (kproc->data->uses_lreset)
> +		return ret;
> +
>  	ret = kproc->ti_sci->ops.dev_ops.put_device(kproc->ti_sci,
>  						    kproc->ti_sci_id);
>  	if (ret) {
> @@ -192,6 +195,9 @@ static int k3_dsp_rproc_release(struct k3_dsp_rproc *kproc)
>  	struct device *dev = kproc->dev;
>  	int ret;
>  
> +	if (kproc->data->uses_lreset)
> +		goto lreset;
> +
>  	ret = kproc->ti_sci->ops.dev_ops.get_device(kproc->ti_sci,
>  						   kproc->ti_sci_id);
>  	if (ret) {
> @@ -199,6 +205,7 @@ static int k3_dsp_rproc_release(struct k3_dsp_rproc *kproc)
>  		return ret;
>  	}
>  
> +lreset:
>  	ret = reset_control_deassert(kproc->reset);
>  	if (ret) {
>  		dev_err(dev, "local-reset deassert failed, ret = %d\n", ret);
> @@ -210,6 +217,63 @@ static int k3_dsp_rproc_release(struct k3_dsp_rproc *kproc)
>  	return ret;
>  }
>  
> +/*
> + * The C66x DSP cores have a local reset that affects only the CPU, and a
> + * generic module reset that powers on the device and allows the DSP internal
> + * memories to be accessed while the local reset is asserted. This function is
> + * used to release the global reset on C66x DSPs to allow loading into the DSP
> + * internal RAMs. The .prepare() ops is invoked by remoteproc core before any
> + * firmware loading, and is followed by the .start() ops after loading to
> + * actually let the C66x DSP cores run. The local reset on C71x cores is a
> + * no-op and the global reset cannot be released on C71x cores until after
> + * the firmware images are loaded, so this function does nothing for C71x cores.
> + */
> +static int k3_dsp_rproc_prepare(struct rproc *rproc)
> +{
> +	struct k3_dsp_rproc *kproc = rproc->priv;
> +	struct device *dev = kproc->dev;
> +	int ret;
> +
> +	/* local reset is no-op on C71x processors */
> +	if (!kproc->data->uses_lreset)
> +		return 0;

In k3_dsp_rproc_release() the condition is "if (kproc->data->uses_lreset)" and
here it is the opposite, which did a good job at getting me confused.

Taking a step back, I assume c71 DSPs will have their own k3_dsp_dev_data where
the users_lreset flag will be false.  In that case I think it would make the
code easier to understand if the k3_dsp_rproc_ops was declared without the
.prepare and .unprepare.  In probe(), if data->uses_lreset is true then
k3_dsp_rproc_prepare() and k3_dsp_rproc_unprepare() are set.

I am done reviewing this set.

Thanks,
Mathieu

> +
> +	ret = kproc->ti_sci->ops.dev_ops.get_device(kproc->ti_sci,
> +						    kproc->ti_sci_id);
> +	if (ret)
> +		dev_err(dev, "module-reset deassert failed, cannot enable internal RAM loading, ret = %d\n",
> +			ret);
> +
> +	return ret;
> +}
> +
> +/*
> + * This function implements the .unprepare() ops and performs the complimentary
> + * operations to that of the .prepare() ops. The function is used to assert the
> + * global reset on applicable C66x cores. This completes the second portion of
> + * powering down the C66x DSP cores. The cores themselves are only halted in the
> + * .stop() callback through the local reset, and the .unprepare() ops is invoked
> + * by the remoteproc core after the remoteproc is stopped to balance the global
> + * reset.
> + */
> +static int k3_dsp_rproc_unprepare(struct rproc *rproc)
> +{
> +	struct k3_dsp_rproc *kproc = rproc->priv;
> +	struct device *dev = kproc->dev;
> +	int ret;
> +
> +	/* local reset is no-op on C71x processors */
> +	if (!kproc->data->uses_lreset)
> +		return 0;
> +
> +	ret = kproc->ti_sci->ops.dev_ops.put_device(kproc->ti_sci,
> +						    kproc->ti_sci_id);
> +	if (ret)
> +		dev_err(dev, "module-reset assert failed, ret = %d\n", ret);
> +
> +	return ret;
> +}
> +
>  /*
>   * Power up the DSP remote processor.
>   *
> @@ -353,6 +417,8 @@ static void *k3_dsp_rproc_da_to_va(struct rproc *rproc, u64 da, size_t len)
>  }
>  
>  static const struct rproc_ops k3_dsp_rproc_ops = {
> +	.prepare	= k3_dsp_rproc_prepare,
> +	.unprepare	= k3_dsp_rproc_unprepare,
>  	.start		= k3_dsp_rproc_start,
>  	.stop		= k3_dsp_rproc_stop,
>  	.kick		= k3_dsp_rproc_kick,
> @@ -644,6 +710,22 @@ static int k3_dsp_rproc_probe(struct platform_device *pdev)
>  		goto disable_clk;
>  	}
>  
> +	/*
> +	 * ensure the DSP local reset is asserted to ensure the DSP doesn't
> +	 * execute bogus code in .prepare() when the module reset is released.
> +	 */
> +	if (data->uses_lreset) {
> +		ret = reset_control_status(kproc->reset);
> +		if (ret < 0) {
> +			dev_err(dev, "failed to get reset status, status = %d\n",
> +				ret);
> +			goto release_mem;
> +		} else if (ret == 0) {
> +			dev_warn(dev, "local reset is deasserted for device\n");
> +			k3_dsp_rproc_reset(kproc);
> +		}
> +	}
> +
>  	ret = rproc_add(rproc);
>  	if (ret) {
>  		dev_err(dev, "failed to add register device with remoteproc core, status = %d\n",
> -- 
> 2.23.0
> 

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