Re: [PATCH v2] [RFC] rcar-vin: rcar-csi2: Correct the selection of hsfreqrange

[Niklas Söderlund]

Hi Suresh,

Thanks for your feedback.

On 2020-03-18 18:00:29 +0900, Suresh Udipi wrote:
> On Tue, Mar 17, 2020 at 11:37:56AM +0100, Niklas Söderlund wrote:
> > Hi Suresh,
> > 
> > Thanks for your work.
> > 
> > On 2020-03-17 16:08:25 +0900, Suresh Udipi wrote:
> > > hsfreqrange should be chosen based on the calculated mbps which
> > > is closer to the default bit rate  and within the range as per
> > > table[1]. But current calculation always selects first value which
> > > is greater than or equal to the calculated mbps which may lead
> > > to chosing a wrong range in some cases.
> > > 
> > > For example for 360 mbps for H3/M3N
> > > Existing logic selects
> > > Calculated value 360Mbps : Default 400Mbps Range [368.125 -433.125 mbps]
> > > 
> > > This hsfreqrange is out of range.
> > > 
> > > The logic is changed to get the default value which is closest to the
> > > calculated value [1]
> > > 
> > > Calculated value 360Mbps : Default 350Mbps  Range [320.625 -380.625 mpbs]
> > > 
> > > [1] specs r19uh0105ej0200-r-car-3rd-generation.pdf [Table 25.9]
> > > 
> > > There is one exectpion value 227Mbps, which may cause out of
> > > range.
> > 
> > Then something else is needed I think :-)
> > 
> > I liked v1 of this RFC more, where you added a u16 min and max to struct 
> > rcsi2_mbps_reg. I think that is the right solution.
> > 
> > What I tried to express in my review of v1 was
> > 
> > - You should remove the mbps member from struct rcsi2_mbps_reg.
> > - Update the walk of the array in rcsi2_set_phypll() so that it finds 
> >   the first entry where the calculated target value is between min and 
> >   max and use the reg setting for that entry.
> > 
> > Would that solution make sens too you? Sorry if I expressed myself a but 
> > muddy in v1 about this.
>  
> Thank you for your feedback. Checking the range make more sense.
> 
> We can further optimize it, by checking only the Max range value.
> 
> - Remove mbps and min member from struct rcsi2_mbps_reg.
> - Update the walk of the array in rcsi2_set_phypll() so that it finds
>   the first entry where the calculated bit rate is less than the max.
> 
> Lower bit rates less than 80Mbps 
> like 48Mbps(Raspberry pi camera 640x480 connected to Kingfisher)
> can also be supported by selecting the lowest default bit rate 80Mbps
> as done before this fix.

I think this approach sounds nice.

> 
> Please let me know your opinion on the same.
> Meanwhile iam working on creating the patch, test it and update the same.

Looking forward to it!

> > > 
> > > Fixes: 769afd212b16 ("media: rcar-csi2: add Renesas R-Car MIPI CSI-2 receiver driver")
> > > 
> > > Signed-off-by: Suresh Udipi <sudipi@xxxxxxxxxxxxxx>
> > > Signed-off-by: Kazuyoshi Akiyama <akiyama@xxxxxxxxxxxxx>
> > > ---
> > > Changes in v2:
> > >   - Added the boundary check for the maximum bit rate.
> > >   
> > >   - Simplified the logic by remmoving range check 
> > >     as only the closest default value covers most 
> > >     of the use cases.
> > > 
> > >   - Aligning the commit message based on the above change
> > > 
> > >  drivers/media/platform/rcar-vin/rcar-csi2.c | 18 +++++++++++++-----
> > >  1 file changed, 13 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c b/drivers/media/platform/rcar-vin/rcar-csi2.c
> > > index faa9fb2..6573625 100644
> > > --- a/drivers/media/platform/rcar-vin/rcar-csi2.c
> > > +++ b/drivers/media/platform/rcar-vin/rcar-csi2.c
> > > @@ -199,6 +199,7 @@ static const struct rcsi2_mbps_reg phtw_mbps_v3m_e3[] = {
> > >  /* PHY Frequency Control */
> > >  #define PHYPLL_REG			0x68
> > >  #define PHYPLL_HSFREQRANGE(n)		((n) << 16)
> > > +#define PHYPLL_HSFREQRANGE_MAX		1500
> > >  
> > >  static const struct rcsi2_mbps_reg hsfreqrange_h3_v3h_m3n[] = {
> > >  	{ .mbps =   80, .reg = 0x00 },
> > > @@ -431,16 +432,23 @@ static int rcsi2_wait_phy_start(struct rcar_csi2 *priv)
> > >  static int rcsi2_set_phypll(struct rcar_csi2 *priv, unsigned int mbps)
> > >  {
> > >  	const struct rcsi2_mbps_reg *hsfreq;
> > > +	const struct rcsi2_mbps_reg *hsfreq_prev = NULL;
> > >  
> > > -	for (hsfreq = priv->info->hsfreqrange; hsfreq->mbps != 0; hsfreq++)
> > > -		if (hsfreq->mbps >= mbps)
> > > -			break;
> > > -
> > > -	if (!hsfreq->mbps) {
> > > +	if (mbps > PHYPLL_HSFREQRANGE_MAX) {
> > >  		dev_err(priv->dev, "Unsupported PHY speed (%u Mbps)", mbps);
> > >  		return -ERANGE;
> > >  	}
> > >  
> > > +	for (hsfreq = priv->info->hsfreqrange; hsfreq->mbps != 0; hsfreq++) {
> > > +		if (hsfreq->mbps >= mbps)
> > > +			break;
> > > +		hsfreq_prev = hsfreq;
> > > +	}
> > > +
> > > +	if (hsfreq_prev &&
> > > +	    ((mbps - hsfreq_prev->mbps) <= (hsfreq->mbps - mbps)))
> > > +		hsfreq = hsfreq_prev;
> > > +
> > >  	rcsi2_write(priv, PHYPLL_REG, PHYPLL_HSFREQRANGE(hsfreq->reg));
> > >  
> > >  	return 0;
> > > -- 
> > > 2.7.4
> > > 
> > 
> > -- 
> > Regards,
> > Niklas Söderlund
> 
> -- 
> Best Regards,
> Suresh Udipi.

-- 
Regards,
Niklas Söderlund