linux-kernel - Re: [PATCH v4 1/6] media: i2c: ov5640: Remain in power down for DVP mode unless streaming

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Date:   Fri, 7 Jan 2022 15:49:52 +0000
From:   "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To:     Eugen Hristev <Eugen.Hristev@...rochip.com>
Cc:     Hugues Fruchet <hugues.fruchet@...com>,
        "Lad, Prabhakar" <prabhakar.mahadev-lad.rj@...renesas.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Steve Longerbeam <slongerbeam@...il.com>,
        Paul <paul.kocialkowski@...tlin.com>,
        linux-media <linux-media@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Subject: Re: [PATCH v4 1/6] media: i2c: ov5640: Remain in power down for DVP
 mode unless streaming

On Tue, Jan 4, 2022 at 9:57 AM Lad, Prabhakar
<prabhakar.csengg@...il.com> wrote:
>
> Hi Eugen,
>
> On Mon, Jan 3, 2022 at 11:29 AM <Eugen.Hristev@...rochip.com> wrote:
> >
> > On 12/21/21 5:11 PM, Lad, Prabhakar wrote:
> > > Hi Eugen,
> > >
<snip>
> > > could you give it a shot with yavta please.
> >
> > Hello Lad,
> >
> > I debugged this further, and I have some news:
> >
> > It looks like the 'write 0x2 to SYS_CLTR0' does not fail itself, rather
> > the sensor refuses to accept a power up.
> >
> > I tried to read the register before the write, and it reads 0x42.
> > Then, I tried to write 0x42 back, and it works fine.
> > So, I do not think there is a problem with i2c communication.
> > The only problem is that the sensor refuses to power up (accept the 0x2
> > into the SYS_CTRL_0 ), due to an unknown (to me) reason.
> >
> That's strange.
>
> > If the power up is performed at the initialization phase, it works.
> >
> > I also tried to capture with v4l2-ctl, and the result is the same.
> >
> you mean yavta ?
>
> > Which of the init configuration set of registers your test is using?
> I have been testing 320x240 and 640x480. Could you give that a try please?
>
> > It may be that it does not work in a specific config .
> >
> > The datasheet which I have does not claim that the 'power up' might fail
> > in some circumstances.
> >
> Let me check if I can ping OmniVision FAE.
>
Fyi.. I got the below feedback from OmniVision FAE.

SW standby bit is working as expected from my side.


As far as the sensor initialization is concerned  we use HW power up
sequence defined in the datasheet followed by SW initialization.

SW initialization consist of the following :-

78 3103  11    ;  I2C timing ( do not modify)
78 3008  82  ;   SW reset
78 3008  42  ;   Stop streaming
78 …….            Sensor settings for required mode

78 3008  02  ;   Start  streaming

Note:-  0x3008[7]  SW reset bit is volatile, as soon as a reset is
applied the  all the bits  are  cleared  and  0x3008[7:0] set to
default value hence  should read  0x2

Cheers,
Prabhakar