linux-kernel - Re: [RFC V2 2/2] phy: freescale: fsl-samsung-hdmi: Support dynamic integer divider

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Message-ID: <ZtF69NSHFtAwDupq@vaman>
Date: Fri, 30 Aug 2024 13:25:32 +0530
From: Vinod Koul <vkoul@...nel.org>
To: Adam Ford <aford173@...il.com>
Cc: linux-phy@...ts.infradead.org, dominique.martinet@...ark-techno.com,
	linux-imx@....com, festevam@...il.com, frieder.schrempf@...tron.de,
	aford@...conembedded.com,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Lucas Stach <l.stach@...gutronix.de>,
	Marco Felsch <m.felsch@...gutronix.de>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC V2 2/2] phy: freescale: fsl-samsung-hdmi: Support dynamic
 integer divider

On 29-08-24, 13:30, Adam Ford wrote:
> On Thu, Aug 29, 2024 at 12:56 PM Vinod Koul <vkoul@...nel.org> wrote:
> >
> > On 28-08-24, 21:12, Adam Ford wrote:
> > > There is currently a look-up table for a variety of resolutions.
> > > Since the phy has the ability to dynamically calculate the values
> > > necessary to use the intger divider which should allow more
> > > resolutions without having to update the look-up-table.  If the
> > > integer calculator cannot get an exact frequency, it falls back
> > > to the look-up-table.  Because the LUT algorithm does some
> > > rounding, I did not remove integer entries from the LUT.
> >
> > Any reason why this is RFC?
> 
> Someone was asking for functionality, but I'm not 100% sure this is
> the right approach or it would even work.  I am waiting for feedback
> from Dominique to determine if this helps solve the display for that
> particular display.
> 
> >
> > >
> > > Signed-off-by: Adam Ford <aford173@...il.com>
> > >
> > > diff --git a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> > > index bc5d3625ece6..76e0899c6006 100644
> > > --- a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> > > +++ b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> > > @@ -16,6 +16,8 @@
> > >
> > >  #define PHY_REG(reg)         (reg * 4)
> > >
> > > +#define REG01_PMS_P_MASK     GENMASK(3, 0)
> > > +#define REG03_PMS_S_MASK     GENMASK(7, 4)
> > >  #define REG12_CK_DIV_MASK    GENMASK(5, 4)
> > >  #define REG13_TG_CODE_LOW_MASK       GENMASK(7, 0)
> > >  #define REG14_TOL_MASK               GENMASK(7, 4)
> > > @@ -31,11 +33,17 @@
> > >
> > >  #define PHY_PLL_DIV_REGS_NUM 6
> > >
> > > +#ifndef MHZ
> > > +#define MHZ  (1000UL * 1000UL)
> > > +#endif
> > > +
> > >  struct phy_config {
> > >       u32     pixclk;
> > >       u8      pll_div_regs[PHY_PLL_DIV_REGS_NUM];
> > >  };
> > >
> > > +static struct phy_config custom_phy_pll_cfg;
> > > +
> > >  static const struct phy_config phy_pll_cfg[] = {
> > >       {
> > >               .pixclk = 22250000,
> > > @@ -440,10 +448,83 @@ fsl_samsung_hdmi_phy_configure_pll_lock_det(struct fsl_samsung_hdmi_phy *phy,
> > >              phy->regs + PHY_REG(14));
> > >  }
> > >
> > > +static unsigned long fsl_samsung_hdmi_phy_find_pms(unsigned long fout, u8 *p, u16 *m, u8 *s)
> > > +{
> > > +     unsigned long best_freq = 0;
> > > +     u32 min_delta = 0xffffffff;
> >
> > > +     u8 _p, best_p;
> > > +     u16 _m, best_m;
> > > +     u8 _s, best_s;
> > > +
> > > +     for (_p = 1; _p <= 11; ++_p) {
> >
> > starts with 1 to 11.. why?
> 
> According to Rev 2 of the 8MP Reference Manual, the Previder range is
> between 1 and 11.

Would be better to document these assumptions, am sure if someone asks
you this next year, it would be hard to recall :-)

-- 
~Vinod