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Re: [PATCH] i2c: aspeed: Retain delay/setup/hold values when configuring bus frequency

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On Tue, Aug 15, 2017 at 10:21 AM, Andrew Jeffery <andrew@aj.id.au> wrote:
> In addition to the base, low and high clock configuration, the AC timing
> register #1 on the AST2400 houses fields controlling:
>
> 1. tBUF: Minimum delay between Stop and Start conditions
> 2. tHDSTA: Hold time for the Start condition
> 3. tACST: Setup time for Start and Stop conditions, and hold time for the
>    Repeated Start condition
>
> These values are defined in hardware on the AST2500 and therefore don't
> need to be set.
>
> aspeed_i2c_init_clk() was performing a direct write of the generated
> clock values rather than a read/mask/modify/update sequence to retain
> tBUF, tHDSTA and tACST, and therefore cleared the tBUF, tHDSTA and tACST
> fields on the AST2400. This resulted in a delay/setup/hold time of 1
> base clock, which in some configurations is not enough for some devices
> (e.g. the MAX31785 fan controller, with an APB of 48MHz and a desired
> bus speed of 100kHz).
>
> Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
> ---
>  drivers/i2c/busses/i2c-aspeed.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
> index ee76e6dddc4b..284f8670dbeb 100644
> --- a/drivers/i2c/busses/i2c-aspeed.c
> +++ b/drivers/i2c/busses/i2c-aspeed.c
> @@ -53,6 +53,9 @@
>  #define ASPEED_I2CD_MASTER_EN                          BIT(0)
>
>  /* 0x04 : I2CD Clock and AC Timing Control Register #1 */
> +#define ASPEED_I2CD_TIME_TBUF_MASK                     GENMASK(31, 28)
> +#define ASPEED_I2CD_TIME_THDSTA_MASK                   GENMASK(27, 24)
> +#define ASPEED_I2CD_TIME_TACST_MASK                    GENMASK(23, 20)
>  #define ASPEED_I2CD_TIME_SCL_HIGH_SHIFT                        16
>  #define ASPEED_I2CD_TIME_SCL_HIGH_MASK                 GENMASK(19, 16)
>  #define ASPEED_I2CD_TIME_SCL_LOW_SHIFT                 12
> @@ -744,7 +747,11 @@ static int aspeed_i2c_init_clk(struct aspeed_i2c_bus *bus)
>         u32 divisor, clk_reg_val;
>
>         divisor = DIV_ROUND_UP(bus->parent_clk_frequency, bus->bus_frequency);
> -       clk_reg_val = bus->get_clk_reg_val(divisor);
> +       clk_reg_val = readl(bus->base + ASPEED_I2C_AC_TIMING_REG1);
> +       clk_reg_val &= (ASPEED_I2CD_TIME_TBUF_MASK |
> +                       ASPEED_I2CD_TIME_THDSTA_MASK |
> +                       ASPEED_I2CD_TIME_TACST_MASK);
> +       clk_reg_val |= bus->get_clk_reg_val(divisor);
>         writel(clk_reg_val, bus->base + ASPEED_I2C_AC_TIMING_REG1);
>         writel(ASPEED_NO_TIMEOUT_CTRL, bus->base + ASPEED_I2C_AC_TIMING_REG2);
>
> --
> 2.11.0
>

Awesome! I think this might fix an issue we saw on one of our boards.
I am out of the country right now, so I cannot test this myself, until Monday.

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[PATCH] i2c: aspeed: Retain delay/setup/hold values when configuring bus frequency Andrew Jeffery <andrew@aj.id.au> - 2017-08-15 09:30 +0200
  Re: [PATCH] i2c: aspeed: Retain delay/setup/hold values when  configuring bus frequency Brendan Higgins <brendanhiggins@google.com> - 2017-08-16 08:40 +0200
  Re: [PATCH] i2c: aspeed: Retain delay/setup/hold values when  configuring bus frequency Joel Stanley <joel@jms.id.au> - 2017-08-16 09:00 +0200
    Re: [PATCH] i2c: aspeed: Retain delay/setup/hold values when  configuring bus frequency Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2017-08-16 09:10 +0200
      Re: [PATCH] i2c: aspeed: Retain delay/setup/hold values when  configuring bus frequency Cédric Le Goater <clg@kaod.org> - 2017-08-16 09:20 +0200
    Re: [PATCH] i2c: aspeed: Retain delay/setup/hold values when  configuring bus frequency Cédric Le Goater <clg@kaod.org> - 2017-08-16 13:40 +0200
  Re: [PATCH] i2c: aspeed: Retain delay/setup/hold values when  configuring bus frequency Brendan Higgins <brendanhiggins@google.com> - 2017-08-24 02:30 +0200

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