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