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

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Message-ID: <CACPK8XeNDxo14KRsAqo3a0Rs26h-1vRsLyqSX+bt2jfZHq=5yA@mail.gmail.com>
Date:   Wed, 16 Aug 2017 16:19:57 +0930
From:   Joel Stanley <joel@....id.au>
To:     Andrew Jeffery <andrew@...id.au>
Cc:     linux-i2c@...r.kernel.org, Wolfram Sang <wsa@...-dreams.de>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        linux-aspeed@...ts.ozlabs.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ryan Chen <ryan_chen@...eedtech.com>
Subject: Re: [PATCH] i2c: aspeed: Retain delay/setup/hold values when
 configuring bus frequency

On Tue, Aug 15, 2017 at 4:51 PM, Andrew Jeffery <andrew@...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@...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);

Instead of keeping the u-boot values (which appear to be hard-coded),
should we instead put the known working values in the register?

Cheers,

Joel