linux-kernel - Re: [PATCH v6 4/5] media: i2c: max9286: Make channel amplitude programmable

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Date:   Wed, 16 Dec 2020 19:14:45 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>
Cc:     kieran.bingham+renesas@...asonboard.com,
        laurent.pinchart+renesas@...asonboard.com,
        niklas.soderlund+renesas@...natech.se, geert@...ux-m68k.org,
        linux-media@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hyun Kwon <hyunk@...inx.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        sergei.shtylyov@...il.com
Subject: Re: [PATCH v6 4/5] media: i2c: max9286: Make channel amplitude
 programmable

On Wed, Dec 16, 2020 at 07:14:25PM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
> 
> Thank you for the patch.
> 
> On Tue, Dec 15, 2020 at 06:09:56PM +0100, Jacopo Mondi wrote:
> > Instrument the function that configures the reverse channel with a
> > programmable amplitude value.
> > 
> > This change serves to prepare to adjust the reverse channel amplitude
> > depending on the remote end high-threshold configuration.
> > 
> > Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> > ---
> >  drivers/media/i2c/max9286.c | 22 ++++++++++++++++------
> >  1 file changed, 16 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> > index 1cfc8801c0b2..021309c6dd6f 100644
> > --- a/drivers/media/i2c/max9286.c
> > +++ b/drivers/media/i2c/max9286.c
> > @@ -336,19 +336,29 @@ static void max9286_configure_i2c(struct max9286_priv *priv, bool localack)
> >  	usleep_range(3000, 5000);
> >  }
> >  
> > -static void max9286_reverse_channel_setup(struct max9286_priv *priv)
> > +static void max9286_reverse_channel_setup(struct max9286_priv *priv,
> > +					  unsigned int chan_amplitude)
> >  {
> > +	/* Reverse channel transmission time: default to 1. */
> > +	u8 chan_config = MAX9286_REV_TRF(1);
> > +
> >  	/*
> >  	 * Reverse channel setup.
> >  	 *
> >  	 * - Enable custom reverse channel configuration (through register 0x3f)
> >  	 *   and set the first pulse length to 35 clock cycles.
> > -	 * - Increase the reverse channel amplitude to 170mV to accommodate the
> > -	 *   high threshold enabled by the serializer driver.
> > +	 * - Adjust reverse channel amplitude: values > 130 are programmed
> > +	 *   using the additional +100mV REV_AMP_X boost flag
> >  	 */
> >  	max9286_write(priv, 0x3f, MAX9286_EN_REV_CFG | MAX9286_REV_FLEN(35));
> > -	max9286_write(priv, 0x3b, MAX9286_REV_TRF(1) | MAX9286_REV_AMP(70) |
> > -		      MAX9286_REV_AMP_X);
> > +
> > +	if (chan_amplitude > 100) {
> > +		/* It is not possible to express values (100 < x < 130) */
> > +		chan_amplitude = chan_amplitude < 130
> > +			       ? 30 : chan_amplitude - 100;
> 
> This could also be written
> 
> 		chan_amplitude = min(30, chan_amplitude - 100);

s/min/max/ of course.

> 
> With or without the change,
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> 
> > +		chan_config |= MAX9286_REV_AMP_X;
> > +	}
> > +	max9286_write(priv, 0x3b, chan_config | MAX9286_REV_AMP(chan_amplitude));
> >  	usleep_range(2000, 2500);
> >  }
> >  
> > @@ -957,7 +967,7 @@ static int max9286_setup(struct max9286_priv *priv)
> >  	 * only. This should be disabled after the mux is initialised.
> >  	 */
> >  	max9286_configure_i2c(priv, true);
> > -	max9286_reverse_channel_setup(priv);
> > +	max9286_reverse_channel_setup(priv, 170);
> >  
> >  	/*
> >  	 * Enable GMSL links, mask unused ones and autodetect link

-- 
Regards,

Laurent Pinchart