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Date: Wed, 18 Mar 2020 11:19:36 +0100
From: Niklas Söderlund
<niklas.soderlund@...natech.se>
To: Suresh Udipi <sudipi@...adit-jv.com>
Cc: akiyama@...-osk.co.jp, efriedrich@...adit-jv.com,
erosca@...adit-jv.com, hverkuil-cisco@...all.nl,
jacopo+renesas@...ndi.org, laurent.pinchart@...asonboard.com,
linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
linux-renesas-soc@...r.kernel.org, mrodin@...adit-jv.com,
securitycheck@...so.co.jp
Subject: Re: [PATCH v2] [RFC] rcar-vin: rcar-csi2: Correct the selection of
hsfreqrange
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@...adit-jv.com>
> > > Signed-off-by: Kazuyoshi Akiyama <akiyama@...-osk.co.jp>
> > > ---
> > > 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
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