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

[Hangxiang Ma <hangxiang.ma@oss.qualcomm.com>]

On 10/21/2026 4:53 PM, Bryan O'Donoghue wrote:
> 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

Hi Loic, Bryan, thanks for the review. I wonder if it would be better to 
keep the check on the CSID side?

vfe->reg_update() is also used outside stream-on, such as bufdone, queue 
buffer. It must be implemented in VFE. We only want to change the VFE 
behavior at stream-on stage, in function vfe_enable_output_v2(). So 
making vfe->reg_update() optional could affect runtime updates.

Maybe the cheapest way is still to check the CSID side reg_update 
implementation at stream-on stage? I'm very glad to hear your 
suggestions. Thanks a lot.

---
Best Regards,
Hangxiang