Re: [PATCH v3 2/8] media: qcom: camss: csiphy-3ph: Use odd bits for configuring C-PHY lanes

[Kieran Bingham <kieran.bingham@ideasonboard.com>]

Quoting Bryan O'Donoghue (2026-01-17 21:38:17)
> On 17/01/2026 15:36, David Heidelberg via B4 Relay wrote:
> > From: David Heidelberg <david@ixit.cz>
> > 
> > So far, only D-PHY mode was supported, which uses even bits when enabling
> > or masking lanes. For C-PHY configuration, the hardware instead requires
> > using the odd bits.
> > 
> > Since there can be unrecognized configuration allow returning failure.
> > 
> > Signed-off-by: David Heidelberg <david@ixit.cz>
> > ---
> >   .../platform/qcom/camss/camss-csiphy-2ph-1-0.c     |  8 ++--
> >   .../platform/qcom/camss/camss-csiphy-3ph-1-0.c     | 49 +++++++++++++++++-----
> >   drivers/media/platform/qcom/camss/camss-csiphy.c   |  4 +-
> >   drivers/media/platform/qcom/camss/camss-csiphy.h   |  6 +--
> >   4 files changed, 47 insertions(+), 20 deletions(-)
> > 
> > diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c
> > index 9d67e7fa6366a..bb4b91f69616b 100644
> > --- a/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c
> > +++ b/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c
> > @@ -94,9 +94,9 @@ static u8 csiphy_settle_cnt_calc(s64 link_freq, u32 timer_clk_rate)
> >       return settle_cnt;
> >   }
> >   
> > -static void csiphy_lanes_enable(struct csiphy_device *csiphy,
> > -                             struct csiphy_config *cfg,
> > -                             s64 link_freq, u8 lane_mask)
> > +static int csiphy_lanes_enable(struct csiphy_device *csiphy,
> > +                            struct csiphy_config *cfg,
> > +                            s64 link_freq, u8 lane_mask)
> >   {
> >       struct csiphy_lanes_cfg *c = &cfg->csi2->lane_cfg;
> >       u8 settle_cnt;
> > @@ -132,6 +132,8 @@ static void csiphy_lanes_enable(struct csiphy_device *csiphy,
> >               writel_relaxed(0x3f, csiphy->base +
> >                              CAMSS_CSI_PHY_INTERRUPT_CLEARn(l));
> >       }
> > +
> > +     return 0;
> >   }
> >   
> >   static void csiphy_lanes_disable(struct csiphy_device *csiphy,
> > diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> > index 4154832745525..f3a8625511e1e 100644
> > --- a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> > +++ b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> > @@ -14,6 +14,7 @@
> >   #include <linux/delay.h>
> >   #include <linux/interrupt.h>
> >   #include <linux/io.h>
> > +#include <linux/media-bus-format.h>
> >   
> >   #define CSIPHY_3PH_LNn_CFG1(n)                      (0x000 + 0x100 * (n))
> >   #define CSIPHY_3PH_LNn_CFG1_SWI_REC_DLY_PRG (BIT(7) | BIT(6))
> > @@ -993,13 +994,22 @@ static void csiphy_gen2_config_lanes(struct csiphy_device *csiphy,
> >   
> >   static u8 csiphy_get_lane_mask(struct csiphy_lanes_cfg *lane_cfg)
> >   {
> > -     u8 lane_mask;
> > -     int i;
> > +     u8 lane_mask = 0;
> >   
> > -     lane_mask = CSIPHY_3PH_CMN_CSI_COMMON_CTRL5_CLK_ENABLE;
> > +     switch (lane_cfg->phy_cfg) {
> > +     case V4L2_MBUS_CSI2_CPHY:
> > +             for (int i = 0; i < lane_cfg->num_data; i++)
> > +                     lane_mask |= (1 << lane_cfg->data[i].pos) + 1;
> 
> 1 << anything == BIT(anything)
> 
> I've always disliked the look of this code and now it occurs to me why.
> 
> This code is analogous to:
> 
> lane_mask |= BIT(lane_cfg->data[i].pos) + 1);

I see that addition to a bit mask and get a little bit scared.

This gives:
  pos   mask
   0    0b00000010 (note 0 bit is zero here but 1 on all others)
   1    0b00000011
   2    0b00000101
   3    0b00001001
   4    0b00010001

Is that expected?

Can data[i].pos ever be position 0 ??

I assume this starts at position 1 - and the +1 here is to always set
the zeroth bit ?

Perhapse this might be precise to convey that in such a case?

  lane_mask |= BIT(pos) | 1;

I guess it depends on what this is really being used for which I don't
have in my context.

--
Kieran

 

> 
> but BIT() is less janky and more upstreamy.
> 
> janky/upstreamy - this is the on-point technical argument y'all came 
> here for :)
> 
> > +             break;
> > +     case V4L2_MBUS_CSI2_DPHY:
> > +             lane_mask = CSIPHY_3PH_CMN_CSI_COMMON_CTRL5_CLK_ENABLE;
> >   
> > -     for (i = 0; i < lane_cfg->num_data; i++)
> > -             lane_mask |= 1 << lane_cfg->data[i].pos;
> > +             for (int i = 0; i < lane_cfg->num_data; i++)
> > +                     lane_mask |= 1 << lane_cfg->data[i].pos;
> > +             break;
> > +     default:
> > +             break;
> > +     }
> >   
> >       return lane_mask;
> >   }
> > @@ -1027,10 +1037,11 @@ static bool csiphy_is_gen2(u32 version)
> >       return ret;
> >   }
> >   
> > -static void csiphy_lanes_enable(struct csiphy_device *csiphy,
> > -                             struct csiphy_config *cfg,
> > -                             s64 link_freq, u8 lane_mask)
> > +static int csiphy_lanes_enable(struct csiphy_device *csiphy,
> > +                            struct csiphy_config *cfg,
> > +                            s64 link_freq, u8 lane_mask)
> >   {
> > +     struct device *dev = csiphy->camss->dev;
> >       struct csiphy_lanes_cfg *c = &cfg->csi2->lane_cfg;
> >       struct csiphy_device_regs *regs = csiphy->regs;
> >       u8 settle_cnt;
> > @@ -1039,9 +1050,23 @@ static void csiphy_lanes_enable(struct csiphy_device *csiphy,
> >   
> >       settle_cnt = csiphy_settle_cnt_calc(link_freq, csiphy->timer_clk_rate);
> >   
> > -     val = CSIPHY_3PH_CMN_CSI_COMMON_CTRL5_CLK_ENABLE;
> > -     for (i = 0; i < c->num_data; i++)
> > -             val |= BIT(c->data[i].pos * 2);
> > +     val = 0;
> > +
> > +     switch (c->phy_cfg) {
> > +     case V4L2_MBUS_CSI2_CPHY:
> > +             for (i = 0; i < c->num_data; i++)
> > +                     val |= BIT((c->data[i].pos * 2) + 1);
> > +             break;
> > +     case V4L2_MBUS_CSI2_DPHY:
> > +             val = CSIPHY_3PH_CMN_CSI_COMMON_CTRL5_CLK_ENABLE;
> > +
> > +             for (i = 0; i < c->num_data; i++)
> > +                     val |= BIT(c->data[i].pos * 2);
> > +             break;
> > +     default:
> > +             dev_err(dev, "Unsupported bus type %d\n", c->phy_cfg);
> > +             return -EINVAL;
> > +     }
> >   
> >       writel_relaxed(val, csiphy->base +
> >                      CSIPHY_3PH_CMN_CSI_COMMON_CTRLn(regs->offset, 5));
> > @@ -1068,6 +1093,8 @@ static void csiphy_lanes_enable(struct csiphy_device *csiphy,
> >               writel_relaxed(0, csiphy->base +
> >                              CSIPHY_3PH_CMN_CSI_COMMON_CTRLn(regs->offset, i));
> >       }
> > +
> > +     return 0;
> >   }
> >   
> >   static void csiphy_lanes_disable(struct csiphy_device *csiphy,
> > diff --git a/drivers/media/platform/qcom/camss/camss-csiphy.c b/drivers/media/platform/qcom/camss/camss-csiphy.c
> > index 62623393f4144..08dd238e52799 100644
> > --- a/drivers/media/platform/qcom/camss/camss-csiphy.c
> > +++ b/drivers/media/platform/qcom/camss/camss-csiphy.c
> > @@ -295,9 +295,7 @@ static int csiphy_stream_on(struct csiphy_device *csiphy)
> >               wmb();
> >       }
> >   
> > -     csiphy->res->hw_ops->lanes_enable(csiphy, cfg, link_freq, lane_mask);
> > -
> > -     return 0;
> > +     return csiphy->res->hw_ops->lanes_enable(csiphy, cfg, link_freq, lane_mask);
> 
> ick.
> 
> More high brow stuff from bod here but, more seriously this is three 
> levels of indirection deep and the statement keeps getting longer.
> 
> Could you get a pointer to hw_ops() to reduce this down a bit.
> 
> >   }
> >   
> >   /*
> > diff --git a/drivers/media/platform/qcom/camss/camss-csiphy.h b/drivers/media/platform/qcom/camss/camss-csiphy.h
> > index d198171700e73..21cf2ce931c1d 100644
> > --- a/drivers/media/platform/qcom/camss/camss-csiphy.h
> > +++ b/drivers/media/platform/qcom/camss/camss-csiphy.h
> > @@ -73,9 +73,9 @@ struct csiphy_hw_ops {
> >       void (*hw_version_read)(struct csiphy_device *csiphy,
> >                               struct device *dev);
> >       void (*reset)(struct csiphy_device *csiphy);
> > -     void (*lanes_enable)(struct csiphy_device *csiphy,
> > -                          struct csiphy_config *cfg,
> > -                          s64 link_freq, u8 lane_mask);
> > +     int (*lanes_enable)(struct csiphy_device *csiphy,
> > +                         struct csiphy_config *cfg,
> > +                         s64 link_freq, u8 lane_mask);
> >       void (*lanes_disable)(struct csiphy_device *csiphy,
> >                             struct csiphy_config *cfg);
> >       irqreturn_t (*isr)(int irq, void *dev);
> > 
> 
> With those tweaks.
> 
> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
> 
> ---
> bod