Re: [PATCH v2] interconnect: qcom: implement get_bw with rpmh_read

[Maulik Shah <maulik.shah@oss.qualcomm.com>]

On 08-09-2026 13:39, Neil Armstrong wrote:
> Since we can actually read back the APPS rpmh interconnect
> BCM votes we can actually implement the get_bw() callback
> and provide a coherent average and peak bandwidth at probe time.
>
> The benefits of that are:
> - keep disabled BCMs disabled
> - avoid voting unused BCMs to INT_MAX
>
> If the interconnects are correctly described for a platform,
> all the required BCMs would be voted to the maximum bandwidth
> until sync_state is reached.
>
> Since we only get the BCM vote, we need to redistribute
> the vote values to the associated nodes. The initial BCM
> votes are read back at probe time in order to be ready when
> the get_bw() is called when a node is added.
>
> Tested-by: Georgi Djakov <djakov@kernel.org> #db845c
> Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
> ---
> Changes in v2:
> - Added tested-by
> - Rebased on v7.3-rc1 now the rpmh_read() is merged
> - Link to v1: https://patch.msgid.link/20251106-topic-sm8x50-icc-read-rpmh-v1-1-d03a2e5ca5f7@linaro.org
> ---
>  drivers/interconnect/qcom/bcm-voter.c | 36 +++++++++++++++++++++
>  drivers/interconnect/qcom/bcm-voter.h |  1 +
>  drivers/interconnect/qcom/icc-rpmh.c  | 60 ++++++++++++++++++++++++++++++++++-
>  3 files changed, 96 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/interconnect/qcom/bcm-voter.c b/drivers/interconnect/qcom/bcm-voter.c
> index a2d437a05a11..9014bf20adad 100644
> --- a/drivers/interconnect/qcom/bcm-voter.c
> +++ b/drivers/interconnect/qcom/bcm-voter.c
> @@ -261,6 +261,42 @@ void qcom_icc_bcm_voter_add(struct bcm_voter *voter, struct qcom_icc_bcm *bcm)
>  }
>  EXPORT_SYMBOL_GPL(qcom_icc_bcm_voter_add);
>  
> +/**
> + * qcom_icc_bcm_get_bw - get current bcm vote
> + * @voter: voter used to query bcm
> + * @bcm: bcm to get current vote from
> + */
> +void qcom_icc_bcm_get_bw(struct bcm_voter *voter,
> +			 struct qcom_icc_bcm *bcm)
> +{
> +	struct tcs_cmd cmd = { .addr = bcm->addr };
> +	int ret, i;
> +	u64 x, y;
> +
> +	mutex_lock(&voter->lock);
> +
> +	rpmh_invalidate(voter->dev);

Don't see why rpmh_invalidate() is needed before a read request.

Thanks,
Maulik

> +
> +	ret = rpmh_read(voter->dev, &cmd);
> +	if (ret) {
> +		pr_err("Error sending AMC RPMH requests (%d)\n", ret);
> +		goto out;
> +	}
> +
>