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

[Neil Armstrong <neil.armstrong@linaro.org>]

On 9/8/26 16:39, Maulik Shah wrote:
> 
> 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.

You're right, will drop.

Thanks,
Neil

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