Re: [PATCH v21 04/14] media: qcom: camss: Issue stream-on REG_UPDATE from CSID

[Bryan O'Donoghue <bryan.odonoghue@linaro.org>]

On 21/10/2026 08:37, Wenmeng Liu wrote:
> 
> Hi Bryan, Hangxiang,
> 
> On 10/12/2026 2:45 PM, Hangxiang Ma wrote:
>> On stream-on, CAMSS starts the subdevices upstream from the video node
>> through their sink pads, so the VFE is started before the CSID.
>>
>> Starting with CSID 680, the REG_UPDATE is issued through the CSID
>> rather than the VFE. However, vfe_enable_output_v2() still issues a
>> REG_UPDATE after queueing each initial buffer, before the CSID has
>> configured the stream. The VFE then never signals BUF_DONE. Therefore,
>> the CAMSS now issues the REG_UPDATE from configure_stream() on CSID 680
>> and CSID Gen3 instead. The operation happens after the RX configuration
>> and before the RDI path is enabled.
>>
>> Skip the VFE-side stream-on REG_UPDATE only when the CSID connected to
>> the VFE sink pad implements the reg_update callback. Platforms whose
>> CSID does not provide this callback, as well as lines fed by ISPIF,
>> keep the existing VFE-side REG_UPDATE.
>>
>> Signed-off-by: Hangxiang Ma <hangxiang.ma@oss.qualcomm.com>
>> ---
>>   drivers/media/platform/qcom/camss/camss-csid-680.c |  3 ++
>>   .../media/platform/qcom/camss/camss-csid-gen3.c    |  3 ++
>>   drivers/media/platform/qcom/camss/camss-vfe.c      | 37 ++++++++++++ 
>> +++++++++-
>>   3 files changed, 42 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/media/platform/qcom/camss/camss-csid-680.c b/ 
>> drivers/media/platform/qcom/camss/camss-csid-680.c
>> index 345a67c8fb94..556cdfef6207 100644
>> --- a/drivers/media/platform/qcom/camss/camss-csid-680.c
>> +++ b/drivers/media/platform/qcom/camss/camss-csid-680.c
>> @@ -296,6 +296,8 @@ static void __csid_configure_rdi_stream(struct 
>> csid_device *csid, u8 enable, u8
>>       writel(val, csid->base + CSID_RDI_CFG0(port));
>>   }
>> +static void csid_subdev_reg_update(struct csid_device *csid, int 
>> port_id, bool is_clear);
>> +
>>   static void csid_configure_stream(struct csid_device *csid, u8 enable)
>>   {
>>       int i;
>> @@ -307,6 +309,7 @@ static void csid_configure_stream(struct 
>> csid_device *csid, u8 enable)
>>           if (csid->phy.en_vc & BIT(i)) {
>>               __csid_configure_rdi_stream(csid, enable, i, 0);
>>               __csid_configure_rx(csid, &csid->phy, 0);
>> +            csid_subdev_reg_update(csid, i, false);
>>               __csid_ctrl_rdi(csid, enable, i);
>>           }
>>       }
>> diff --git a/drivers/media/platform/qcom/camss/camss-csid-gen3.c b/ 
>> drivers/media/platform/qcom/camss/camss-csid-gen3.c
>> index 0fdbf75fb27d..830c9c818d3d 100644
>> --- a/drivers/media/platform/qcom/camss/camss-csid-gen3.c
>> +++ b/drivers/media/platform/qcom/camss/camss-csid-gen3.c
>> @@ -219,6 +219,8 @@ static void __csid_configure_rdi_stream(struct 
>> csid_device *csid, u8 enable, u8
>>       writel(val, csid->base + CSID_RDI_CFG0(port));
>>   }
>> +static void csid_subdev_reg_update(struct csid_device *csid, int 
>> port_id, bool is_clear);
>> +
>>   static void csid_configure_stream(struct csid_device *csid, u8 enable)
>>   {
>>       u8 i;
>> @@ -230,6 +232,7 @@ static void csid_configure_stream(struct 
>> csid_device *csid, u8 enable)
>>           if (csid->phy.en_vc & BIT(i)) {
>>               __csid_configure_rdi_stream(csid, enable, i, 0);
>>               __csid_configure_rx(csid, &csid->phy, 0);
>> +            csid_subdev_reg_update(csid, i, false);
>>               __csid_ctrl_rdi(csid, enable, i);
>>           }
>>   }
>> diff --git a/drivers/media/platform/qcom/camss/camss-vfe.c b/drivers/ 
>> media/platform/qcom/camss/camss-vfe.c
>> index 2680a9914765..16a0b5663fe2 100644
>> --- a/drivers/media/platform/qcom/camss/camss-vfe.c
>> +++ b/drivers/media/platform/qcom/camss/camss-vfe.c
>> @@ -502,6 +502,37 @@ void vfe_buf_done(struct vfe_device *vfe, int wm)
>>       spin_unlock_irqrestore(&vfe->output_lock, flags);
>>   }
>> +/*
>> + * vfe_upstream_csid_has_reg_update - Check whether the CSID feeding 
>> this line
>> + * issues its own streamon RUP (i.e. its configure_stream does the RUP).
>> + *
>> + * The CSID->VFE link is created in camss.c for all CSIDs and VFEs, 
>> so the
>> + * upstream entity of the sink pad is either a CSID (possibly with 
>> RUP) or an
>> + * ISPIF (no RUP). Only enabled links are considered.
>> + */
>> +static bool vfe_upstream_csid_has_reg_update(struct vfe_line *line)
>> +{
>> +    struct vfe_device *vfe = to_vfe(line);
>> +    struct camss *camss = vfe->camss;
>> +    struct media_pad *remote;
>> +    unsigned int i;
>> +
>> +    remote = media_pad_remote_pad_first(&line->pads[MSM_VFE_PAD_SINK]);
>> +    if (!remote || !is_media_entity_v4l2_subdev(remote->entity))
>> +        return false;
>> +
>> +    for (i = 0; i < camss->res->csid_num; i++) {
>> +        struct csid_device *csid = &camss->csid[i];
>> +
>> +        if (&csid->subdev.entity != remote->entity)
>> +            continue;
>> +
>> +        return !!csid->res->hw_ops->reg_update;
>> +    }
>> +
>> +    return false;
>> +}
>> +
>>   int vfe_enable_output_v2(struct vfe_line *line)
>>   {
>>       struct vfe_device *vfe = to_vfe(line);
>> @@ -511,6 +542,7 @@ int vfe_enable_output_v2(struct vfe_line *line)
>>       unsigned long flags;
>>       unsigned int frame_skip = 0;
>>       unsigned int i;
>> +    bool rup_in_csid;
>>       sensor_pad = camss_find_sensor_pad(&line->subdev.entity);
>>       if (sensor_pad) {
>> @@ -523,6 +555,8 @@ int vfe_enable_output_v2(struct vfe_line *line)
>>               frame_skip = VFE_FRAME_DROP_VAL - 1;
>>       }
>> +    rup_in_csid = vfe_upstream_csid_has_reg_update(line);
>> +
>>       spin_lock_irqsave(&vfe->output_lock, flags);
>>       ops->reg_update_clear(vfe, line->id);
>> @@ -552,7 +586,8 @@ int vfe_enable_output_v2(struct vfe_line *line)
>>           output->gen2.active_num++;
>>           ops->vfe_wm_update(vfe, output->wm_idx[0],
>>                      output->buf[i]->addr[0], line);
>> -        ops->reg_update(vfe, line->id);
>> +        if (!rup_in_csid)
>> +            ops->reg_update(vfe, line->id);
>>       }
>>       spin_unlock_irqrestore(&vfe->output_lock, flags);
>>
> 
> According to the hardware documentation:
> Starting with CSID 680, CAMIF has moved into the CSID. As a result, RUP 
> is now issued by the CSID and propagated to the IFE.
> 
> Starting with CSID 980, software must also set the SET bit in 
> RUP_AUP_CMD after issuing the RUP/AUP command. Otherwise, the hardware 
> ignores the command and the corresponding register update does not take 
> effect.
> 
> 
> Bryan, according to the HW documentation, the change itself is 
> consistent with the required programming sequence. The main question is 
> whether this is the right implementation from the driver perspective, or 
> if there is a cleaner way to handle it.
> 
> I have tested the change on the Hamoa EVK board.
> Tested-by: Wenmeng Liu <wenmeng.liu@oss.qualcomm.com> # Hamoa EVK
> 
> 
> Thanks,
> Wenmeng

OK thank you for the explanation.

OTOH I agree with Loic's statement - it is cleaner to subtract the 
callback and disjunct on its presence than to add a flag to the same 
effect in reverse.

---
bod