linux-kernel - Re: [PATCH v7 3/4] i2c: npcm: use i2c frequency table

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Message-ID: <bad4bd66cuiva4foudw4iv3aqr4475coo3fll357bh4k5xxqpv@n4iqvh5odsjc>
Date: Tue, 19 Nov 2024 23:25:38 +0100
From: Andi Shyti <andi.shyti@...nel.org>
To: Tyrone Ting <warp5tw@...il.com>
Cc: avifishman70@...il.com, tmaimon77@...il.com, tali.perry1@...il.com, 
	venture@...gle.com, yuenn@...gle.com, benjaminfair@...gle.com, 
	andriy.shevchenko@...ux.intel.com, wsa@...nel.org, rand.sec96@...il.com, 
	wsa+renesas@...g-engineering.com, tali.perry@...oton.com, Avi.Fishman@...oton.com, 
	tomer.maimon@...oton.com, KWLIU@...oton.com, JJLIU0@...oton.com, kfting@...oton.com, 
	openbmc@...ts.ozlabs.org, linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 3/4] i2c: npcm: use i2c frequency table

Hi Tyrone,

...

> > > -     /* 100KHz and below: */
> > > -     if (bus_freq_hz <= I2C_MAX_STANDARD_MODE_FREQ) {
> > > -             sclfrq = src_clk_khz / (bus_freq_khz * 4);
> > > -
> > > -             if (sclfrq < SCLFRQ_MIN || sclfrq > SCLFRQ_MAX)
> > > -                     return -EDOM;
> > > -
> > > -             if (src_clk_khz >= 40000)
> > > -                     hldt = 17;
> > > -             else if (src_clk_khz >= 12500)
> > > -                     hldt = 15;
> > > -             else
> > > -                     hldt = 7;
> > > -     }
> > > -
> > > -     /* 400KHz: */
> > > -     else if (bus_freq_hz <= I2C_MAX_FAST_MODE_FREQ) {
> > > -             sclfrq = 0;
> > > +     switch (bus_freq_hz) {
> > > +     case I2C_MAX_STANDARD_MODE_FREQ:
> > > +             smb_timing = smb_timing_100khz;
> > > +             table_size = ARRAY_SIZE(smb_timing_100khz);
> > > +             break;
> > > +     case I2C_MAX_FAST_MODE_FREQ:
> > > +             smb_timing = smb_timing_400khz;
> > > +             table_size = ARRAY_SIZE(smb_timing_400khz);
> > >               fast_mode = I2CCTL3_400K_MODE;
> > > -
> > > -             if (src_clk_khz < 7500)
> > > -                     /* 400KHZ cannot be supported for core clock < 7.5MHz */
> > > -                     return -EDOM;
> > > -
> > > -             else if (src_clk_khz >= 50000) {
> > > -                     k1 = 80;
> > > -                     k2 = 48;
> > > -                     hldt = 12;
> > > -                     dbnct = 7;
> > > -             }
> > > -
> > > -             /* Master or Slave with frequency > 25MHz */
> > > -             else if (src_clk_khz > 25000) {
> > > -                     hldt = clk_coef(src_clk_khz, 300) + 7;
> > > -                     k1 = clk_coef(src_clk_khz, 1600);
> > > -                     k2 = clk_coef(src_clk_khz, 900);
> > > -             }
> > > -     }
> > > -
> > > -     /* 1MHz: */
> > > -     else if (bus_freq_hz <= I2C_MAX_FAST_MODE_PLUS_FREQ) {
> > > -             sclfrq = 0;
> > > +             break;
> > > +     case I2C_MAX_FAST_MODE_PLUS_FREQ:
> > > +             smb_timing = smb_timing_1000khz;
> > > +             table_size = ARRAY_SIZE(smb_timing_1000khz);
> > >               fast_mode = I2CCTL3_400K_MODE;
> > > -
> > > -             /* 1MHZ cannot be supported for core clock < 24 MHz */
> > > -             if (src_clk_khz < 24000)
> > > -                     return -EDOM;
> > > -
> > > -             k1 = clk_coef(src_clk_khz, 620);
> > > -             k2 = clk_coef(src_clk_khz, 380);
> > > -
> > > -             /* Core clk > 40 MHz */
> > > -             if (src_clk_khz > 40000) {
> > > -                     /*
> > > -                      * Set HLDT:
> > > -                      * SDA hold time:  (HLDT-7) * T(CLK) >= 120
> > > -                      * HLDT = 120/T(CLK) + 7 = 120 * FREQ(CLK) + 7
> > > -                      */
> > > -                     hldt = clk_coef(src_clk_khz, 120) + 7;
> > > -             } else {
> > > -                     hldt = 7;
> > > -                     dbnct = 2;
> > > -             }
> > > +             break;
> > > +     default:
> > > +             return -EINVAL;
> >
> > There is here a slight change of behaiour which is not mentioned
> > in the commit log. Before the user could set a bus_freq_hz which
> > had to be <= I2C_MAX_..._MODE_FREQ, while now it has to be
> > precisely that.
> >
> > Do we want to check what the user has set in the DTS?
> 
> The driver checks the bus frequency the user sets in the DTS.

yes, but before it was checking the value within a range, while
now it's checking the exact value.

The difference is that now if you don't set the exact value you
get EINVAL, not before.

Andi