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 David Heidelberg (2026-02-28 22:37:57)
> On 18/01/2026 13:05, Kieran Bingham wrote:
> > 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.
> 
> Ok, I started looking again into the lovely downstream code.
> 
> D-PHY has bits 0b0D_D_D_D
> C-PHY has bits 0b0_C_C_C_
> 
> so for some reason it worked in my usecase without proper lane mask, but 
> the original formula should be
> 
>   -                     lane_mask |= (1 << lane_cfg->data[i].pos) + 1;
>   +                     lane_mask |= (1 << lane_cfg->data[i].pos + 1);
> 
> Thus
> 
> BIT(lane_cfg->data[i].pos + 1);

That looks a lot more sane!

--
Kieran

> 
> > 
> > --
> > 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
> 
> -- 
> David Heidelberg
>