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

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Message-ID: <20240614123345.GN6019@pendragon.ideasonboard.com>
Date: Fri, 14 Jun 2024 15:33:45 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Julien Stephan <jstephan@...libre.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Louis Kuo <louis.kuo@...iatek.com>,
	Phi-bang Nguyen <pnguyen@...libre.com>,
	Florian Sylvestre <fsylvestre@...libre.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

On Fri, Jun 14, 2024 at 12:38:15PM +0200, Julien Stephan wrote:
> Le mer. 12 juin 2024 à 10:06, AngeloGioacchino Del Regno 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?

You don't have to. You can drop that check, and get the link frequency
of the source subdev with v4l2_get_link_freq(), whatever it is.

> > 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?

Does SENINF need to know both the pixel rate and link frequency ?
V4L2_CID_PIXEL_RATE is very ill-defined, at the moment it only makes
sense as a value relative to the sensor pixel array, and doesn't really
apply further down in the pipeline. What information do you need to
program the SENINF ?

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

-- 
Regards,

Laurent Pinchart