linux-kernel - Re: [PATCH v4 3/5] media: platform: mediatek: isp

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Date: Fri, 14 Jun 2024 12:38:15 +0200
From: Julien Stephan <jstephan@...libre.com>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: Louis Kuo <louis.kuo@...iatek.com>, Phi-bang Nguyen <pnguyen@...libre.com>, 
	Florian Sylvestre <fsylvestre@...libre.com>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, Andy Hsieh <andy.hsieh@...iatek.com>, 
	Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org, 
	linux-media@...r.kernel.org, Matthias Brugger <matthias.bgg@...il.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Paul Elder <paul.elder@...asonboard.com>, 
	Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v4 3/5] media: platform: mediatek: isp_30: add mediatek
 ISP3.0 sensor interface

Le mer. 12 juin 2024 à 10:06, AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> a écrit :
>
> Il 10/06/24 16:39, Julien Stephan ha scritto:
[...]
> >>
> >>> +     writel(0x10001, input->base + SENINF_TG1_SEN_CK);
> >>
> >> Unroll this one... this is the TG1 sensor clock divider.
> >>
> >> CLKFL GENMASK(5, 0)
> >> CLKRS GENMASK(13, 8)
> >> CLKCNT GENMASK(21,16)
> >>
> >> Like this, I don't get what you're trying to set, because you're using a fixed
> >> sensor clock rate, meaning that only a handful of camera sensors will be usable.
> >>
> >> Is this 8Mhz? 16? 24? what? :-)
> >>
> >> Two hints:
> >>    - sensor_clk = clk_get_rate(isp_clk) / (tg1_sen_ck_clkcnt + 1);
> >>    - int mtk_seninf_set_sensor_clk(u8 rate_mhz);
> >>
> >> Please :-)
> >
> > Hi Angelo,
> >
> > I think I get your point about not hardcoding the sensor rate, but I
> > am not sure how to use
> > a mtk_seninf_set_sensor_clk(u8 rate_mhz); function.
> >
> > Where would it be called? How is it exposed to the user?
> >
>
> As for where: setup, streaming start, resolution change (which may be covered
> by streaming start anyway, as a change should be calling stop->start anyway).
>
> And for the how is it exposed to the user - well, depends what you mean for user,
> but it's all standard V4L2 API :-)
>
> Last but not least, I can give you another hint....
>
> struct media_entity *entity = (something_here);
> struct media_pad *mpad;
> struct v4l2_subdev *cam_subdev;
> struct v4l2_ctrl *ctl;
> s64 link_frequency, pixel_clock;
>
> if (entity->pads[0].flags & MEDIA_PAD_FL_SINK)
>     return -E_NOT_A_CAMERA_SENSOR_WE_IGNORE_THIS_ONE;
>
> pad = media_pad_remote_pad_first(&entity->pads[0]);
> if (!pad)
>    return -ENOENT;
>
> if (!is_media_entity_v4l2_subdev(pad->entity))
>    return -ENOENT;
>
> if (pad->entity->function != MEDIA_ENT_F_CAM_SENSOR)
>    return -ENOENT;
>

Hi Angelo,

Thank you for the detailed explanation :)
However, I can't make it work because in my case, seninf is connected
to an external ISP
so pad->entity->function == MEDIA_ENT_F_PROC_VIDEO_ISP.

How can I get the pad corresponding to the sensor?


> cam_subdev = media_entity_to_v4l2_subdev(pad->entity);
> ctl = v4l2_ctrl_find(subdev->ctrl_handler, V4L2_CID_PIXEL_RATE);
>

Is this mandatory to implement V4L2_CID_PIXEL_RATE ?
Should I return an error if not found?

> /* multiplier is usually bits per pixel, divider is usually num of lanes */
> link_frequency = v4l2_get_link_freq(cam_subdev->ctrl_handler, multiplier, divider);
> pixel_clock = v4l2_ctrl_g_ctrl_int64(ctl);
>

How to know the sensor clock given link_frequency and pixel_clock?
Can you point me to drivers doing something similar?

Cheers,
Julien
>
> ....now you know what the sensor wants, set the seninf sensor clock accordingly.
>
> Cheers
> Angelo
>
[...]

Cheers
Julien