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Date: Fri, 12 Jun 2020 19:28:06 +0200
From: Michael Rodin <mrodin@...adit-jv.com>
To: Suresh Udipi <sudipi@...adit-jv.com>
CC: Niklas Söderlund <niklas.soderlund@...natech.se>,
<mrodin@...adit-jv.com>, <efriedrich@...adit-jv.com>,
<erosca@...adit-jv.com>, <linux-kernel@...r.kernel.org>,
<linux-media@...r.kernel.org>, <linux-renesas-soc@...r.kernel.org>,
<mchehab@...nel.org>, <michael@...in.online>,
<securitycheck@...so.co.jp>,
Kazuyoshi Akiyama <akiyama@...-osk.co.jp>
Subject: Re: [PATCH v6] media: rcar-csi2: Correct the selection of hsfreqrange
Hi Niklas,
Hi Suresh,
On Fri, Jun 12, 2020 at 12:10:51PM +0900, Suresh Udipi wrote:
> On Wed, Jun 10, 2020 at 03:40:04PM +0200, Niklas Söderlund wrote:
> > Hi Suresh,
> >
> > Thanks for your persistent work!
> >
> > On 2020-06-08 12:25:03 +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]
> > >
> > > Please note that According to Renesas in Table 25.9 the range for
> > > 220 default value is corrected as below
> > >
> > > |Range (Mbps) | Default Bit rate (Mbps) |
> > > -----------------------------------------------
> > > | 197.125-244.125 | 220 |
> > > -----------------------------------------------
> > >
> > > 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>
> > > Signed-off-by: Michael Rodin <mrodin@...adit-jv.com>
> > > ---
> > > 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
> > >
> > >
> > > Changes in v3:
> > > - Added max member from struct rcsi2_mbps_reg.
> > > mbps varialbe cannot be removed from rcsi2_mbps_reg,
> > > since this structure is reused for
> > > phtw_mbps_h3_v3h_m3n/phtw_mbps_v3m_e3 where mbps is
> > > used.
> > >
> > >
> > > - 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.
> > >
> > > - Support 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
> > >
> > > - Alignement of the commit message based on above changes.
> > >
> > > Changes in v4:
> > > - Remove unncessary braces.
> > >
> > > Changes in v5:
> > > - Removed mbps variable in rcsi2_mbps_reg and aligned all
> > > tables accordingly
> > >
> > > Changes in v6
> > > - Renesas correct the range of default value 220Mbps. Now
> > > if we select the nearest value to the default value all
> > > the values are in range. So reverting back to original patch
> > >
> > > - Added warning for values less than Minimum 80Mbps
> > >
> > >
> > > drivers/media/platform/rcar-vin/rcar-csi2.c | 23 ++++++++++++++++++-----
> > > 1 file changed, 18 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c b/drivers/media/platform/rcar-vin/rcar-csi2.c
> > > index 151e6a9..8c502b7 100644
> > > --- a/drivers/media/platform/rcar-vin/rcar-csi2.c
> > > +++ b/drivers/media/platform/rcar-vin/rcar-csi2.c
> > > @@ -199,6 +199,8 @@ 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
> > > +#define PHYPLL_HSFREQRANGE_MIN 80
> > >
> > > static const struct rcsi2_mbps_reg hsfreqrange_h3_v3h_m3n[] = {
> > > { .mbps = 80, .reg = 0x00 },
> > > @@ -431,16 +433,27 @@ 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;
> > > }
> > >
> > > + if (mbps < PHYPLL_HSFREQRANGE_MIN)
> > > + dev_warn(priv->dev, "PHY speed (%u Mbps) less \
> > > + than Min 80Mbps\n", mbps);
> >
> > I would drop this warning.
> >
>
> This was suggested by Michael. Michael is it ok to drop this warning
> as it is not available before this changes also.
>
I strongly disagree. We should keep the warning for the following reasons:
1. Renesas explicitly states in the hardware manual tables, that 80Mbps is
the lowest supported bit rate (I guess, for a good reason), so using
devices with lower bit rates is at our own risk.
2. Failing for mbps > PHYPLL_HSFREQRANGE_MAX with an ERANGE error but
silently succeeding for mbps < PHYPLL_HSFREQRANGE_MIN does not look
consistent. Both values are out of the official hardware specs.
3. Although rcar csi2 seems to work with at least 1 device in the range
mbps < PHYPLL_HSFREQRANGE_MIN, there is no guarantee that ALL devices
work. And from my experience, users are very happy about any warning,
which points them to a possible reason, why their new device does not
work ;)
> > > +
> > > + 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)))
> >
> > Longer lines are now OK [1] and I think it would add to the readability
> > here.
> >
> > > + hsfreq = hsfreq_prev;
> > > +
> >
> > How about
> >
> > 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;
> > hsfreq_prev = hsfreq;
> > }
> >
> > if (!hsfreq->mbps) {
> > dev_err(priv->dev, "Unsupported PHY speed (%u Mbps)", mbps);
> > return -ERANGE;
> > }
> >
> > if (hsfreq_prev && ((mbps - hsfreq_prev->mbps) <= (hsfreq->mbps - mbps)))
> > hsfreq = hsfreq_prev;
> >
> > rcsi2_write(priv, PHYPLL_REG, PHYPLL_HSFREQRANGE(hsfreq->reg));
> >
> > return 0;
> > }
> >
> > > rcsi2_write(priv, PHYPLL_REG, PHYPLL_HSFREQRANGE(hsfreq->reg));
> > >
> > > return 0;
>
> Agreed I will do the changes and update.
> > > --
> > > 2.7.4
> > >
> >
> > 1. https://lkml.org/lkml/2020/5/29/1038
> >
> > --
> > Regards,
> > Niklas Söderlund
>
> --
> Best Regards,
> Suresh Udipi.
--
Best Regards,
Michael
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