Re: [PATCH RFC 0/2] interconnect: qcom: sdm845: Drop the bootloader vote on ALC

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 10/13/26 10:26 PM, yoxcu wrote:
> From: Michael Auer <mick@yoxcu.de>
> 
> On sdm845 the bootloader can leave a vote on the ALC BCM. No icc node
> uses this BCM, so Linux never writes it and the vote stays in force
> through sleep: the SoC never reaches CX collapse or AOSS sleep. Found
> on a OnePlus 6 (rpmh_read() of ALC on the APPS DRV returns 0x2000000f).

ALC essentially translates into "prevent DDR from sleeping to reduce
latency", I don't know what a good framework for that func would be,
but interconnect (even though it has the plumbing for BCMs) doesn't
seem like it.

> This RFC adds a node without consumers on mem_noc that owns the ALC
> BCM, so the provider drops the vote at sync_state like for any other
> BCM. The node needs a new ID in the dt-bindings header. Android's
> sdm845 bus DT has ALC as a node on mc_virt. Mainline has no mc_virt,
> so the node goes on mem_noc next to ACV and MC0.
> 
> On icc-next the provider reads the boot vote back
> (qcom_icc_bcm_get_bw()). The vote seen here has y = 0xf, so with
> enable_mask BIT(0) the node keeps an initial vote until sync_state and
> then votes 0. A boot vote with bit 0 clear would not be seen and would
> stay. GENMASK(3, 0) would match the vote seen here; I do not know
> which value ALC expects.

On msm-4.9, the downstream kernel for sdm845, the driver unconditionally
writes a (x, y) = (12, 0) on the active-only context and (0, 0) on the
remaining ones and that seems to be the right set of values. I don't
know how secret their meaning is, maybe +Mike can help.

Konrad

> Questions:
> - Is a node without consumers and a new binding ID acceptable for
>   this? No other qcom icc driver models ALC.
> - Or should the node use a driver-local index past the binding IDs,
>   so the header is not touched?
> - Or should the bcm-voter clear bootloader votes on BCMs that no node
>   owns? It has no list of such BCMs, and cmd-db has no API to list
>   them.
> 
> Tested on a OnePlus 6 with an sdm845-mainline 7.1-rc1 based kernel.
> That kernel has no vote read-back, so the node started at INT_MAX:
> ALC was voted with y = 1 until sync_state and 0 after it. ALC reads 0
> after boot and suspend reaches CX collapse (qcom_stats cxsd counts).
> The average current in an idle push standby test (Wi-Fi on) was
> 35.6 mA, against 43.7 mA with the ALC vote kept in the sleep set. With
> ALC off in all sets the phone has been in daily use for two weeks with
> no side effects seen. On icc-next both patches were only build tested
> (W=1).
> 
> This is my first kernel submission, feedback on the process is welcome.
> 
> Michael Auer (2):
>   dt-bindings: interconnect: qcom,sdm845: Add MASTER_ALC
>   interconnect: qcom: sdm845: Own the ALC BCM to drop its boot vote
> 
>  drivers/interconnect/qcom/sdm845.c             | 17 +++++++++++++++++
>  include/dt-bindings/interconnect/qcom,sdm845.h |  1 +
>  2 files changed, 18 insertions(+)
> 
> 
> base-commit: 3fd56a2833c22f62eb84297d0dbd47739632f1a0