Re: [PATCH v2 08/11] media: ccs-pll: Add a flag for even PLL multipliers

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Laurent,

On Mon, Apr 21, 2025 at 11:19:24PM +0300, Laurent Pinchart wrote:
> Hi Sakari,
> 
> Thank you for the patch.

Thank you for the review!

> 
> On Thu, Apr 17, 2025 at 09:53:51AM +0300, Sakari Ailus wrote:
> > Some devices (not entirely CCS compliant) only support even PLL
> > multipliers. Add support for this through a PLL flag.
> > 
> > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > ---
> >  drivers/media/i2c/ccs-pll.c | 11 ++++++++++-
> >  drivers/media/i2c/ccs-pll.h |  1 +
> >  2 files changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/i2c/ccs-pll.c b/drivers/media/i2c/ccs-pll.c
> > index ebbc5e323244..3f8153fb4af0 100644
> > --- a/drivers/media/i2c/ccs-pll.c
> > +++ b/drivers/media/i2c/ccs-pll.c
> > @@ -124,9 +124,10 @@ static void print_pll(struct device *dev, const struct ccs_pll *pll)
> >  	dev_dbg(dev, "pixel rate on CSI-2 bus:\t%u\n",
> >  		pll->pixel_rate_csi);
> >  
> > -	dev_dbg(dev, "flags%s%s%s%s%s%s%s%s%s%s\n",
> > +	dev_dbg(dev, "flags%s%s%s%s%s%s%s%s%s%s%s\n",
> >  		pll->flags & PLL_FL(OP_PIX_CLOCK_PER_LANE) ? " op-pix-clock-per-lane" : "",
> >  		pll->flags & PLL_FL(NO_OP_CLOCKS) ? " no-op-clocks" : "",
> > +		pll->flags & PLL_FL(EVEN_PLL_MULTIPLIER) ? " even-pll-multiplier" : "",
> >  		pll->flags & PLL_FL(LANE_SPEED_MODEL) ? " lane-speed" : "",
> >  		pll->flags & PLL_FL(EXT_IP_PLL_DIVIDER) ?
> >  		" ext-ip-pll-divider" : "",
> > @@ -312,6 +313,10 @@ __ccs_pll_calculate_vt_tree(struct device *dev,
> >  	more_mul *= DIV_ROUND_UP(lim_fr->min_pll_multiplier, mul * more_mul);
> >  	dev_dbg(dev, "more_mul2: %u\n", more_mul);
> >  
> > +	if (pll->flags & CCS_PLL_FLAG_EVEN_PLL_MULTIPLIER &&
> > +	    mul & 1 && more_mul & 1)
> 
> Even if not mandated by the C standard, I'd write
> 
> 	    (mul & 1) && (more_mul & 1))
> 
> to make the code easier to read.

I'll address this in v3.

> 
> > +		more_mul <<= 1;
> 
> I'm not sure to get the logic behind this :-/

Multiplying an odd number with an even number results in an even number,
this is what we need if the above flag is set.

> 
> > +
> >  	pll_fr->pll_multiplier = mul * more_mul;
> >  	if (pll_fr->pll_multiplier > lim_fr->max_pll_multiplier) {
> >  		dev_dbg(dev, "pll multiplier %u too high\n",
> > @@ -668,6 +673,10 @@ ccs_pll_calculate_op(struct device *dev, const struct ccs_pll_limits *lim,
> >  	if (!is_one_or_even(i))
> >  		i <<= 1;
> >  
> > +	if (pll->flags & CCS_PLL_FLAG_EVEN_PLL_MULTIPLIER &&
> > +	    mul & 1 && i & 1)
> 
> Same here.
> 
> > +		i <<= 1;
> > +
> >  	dev_dbg(dev, "final more_mul: %u\n", i);
> >  	if (i > more_mul_max) {
> >  		dev_dbg(dev, "final more_mul is bad, max %u\n", more_mul_max);
> > diff --git a/drivers/media/i2c/ccs-pll.h b/drivers/media/i2c/ccs-pll.h
> > index ee206e5b287b..e8297db45460 100644
> > --- a/drivers/media/i2c/ccs-pll.h
> > +++ b/drivers/media/i2c/ccs-pll.h
> > @@ -31,6 +31,7 @@
> >  #define CCS_PLL_FLAG_DUAL_PLL					BIT(8)
> >  #define CCS_PLL_FLAG_OP_SYS_DDR					BIT(9)
> >  #define CCS_PLL_FLAG_OP_PIX_DDR					BIT(10)
> > +#define CCS_PLL_FLAG_EVEN_PLL_MULTIPLIER			BIT(11)
> 
> You could reuse bit 3, as it got dropped in patch 06/11.

I'll move it there, also for the reason that this isn't a CCS flag.

> 
> >  
> >  /**
> >   * struct ccs_pll_branch_fr - CCS PLL configuration (front)
> 

-- 
Regards,

Sakari Ailus