Re: [PATCH v8 7/8] i2c: rk3x: add i2c support for rk3399 soc

Doug Anderson
2016-05-11T17:38:01Z

Hi,

On Tue, May 10, 2016 at 12:31 PM, David Wu <david.wu@rock-chips.com> wrote:
> static void rk3x_i2c_adapt_div(struct rk3x_i2c *i2c, unsigned long clk_rate)
> {
> struct i2c_timings *t = &i2c->t;
> struct rk3x_i2c_calced_timings calc;
> u64 t_low_ns, t_high_ns;
> + u32 val;
> int ret;
>
> - ret = rk3x_i2c_calc_divs(clk_rate, t, &calc);
> + ret = i2c->soc_data->calc_timings(clk_rate, t, &calc);
> WARN_ONCE(ret != 0, "Could not reach SCL freq %u", t->bus_freq_hz);
>
> - clk_enable(i2c->clk);
> + clk_enable(i2c->pclk);
> +
> i2c_writel(i2c, (calc.div_high << 16) | (calc.div_low & 0xffff),
> REG_CLKDIV);
> - clk_disable(i2c->clk);
> +
> + val = i2c_readl(i2c, REG_CON);
> + val &= ~REG_CON_TUNING_MASK;
> + val |= calc.tuning;
> + i2c_writel(i2c, val, REG_CON);

Another subtle bug here. You need to be holding the spinlock here
since you're doing a read-modify-write of a register that is also
touched by the interrupt handler. We never needed it before because
the previous register update wasn't touched by anyone else and it was
a single atomic write.

Also: technically if we are midway through a transfer when all this
happens then there will be a very short period of time when the two
timing-related registers won't match with each other. I have no idea
how much that would matter, but in the very least it seems wise to
minimize the time where they mismatch. So I'd probably write:

spin_lock_irqsave(&i2c->lock, flags);
val = i2c_readl(i2c, REG_CON);
val &= ~REG_CON_TUNING_MASK;
val |= calc.tuning;
i2c_writel(i2c, val, REG_CON);
i2c_writel(i2c, (calc.div_high << 16) | (calc.div_low & 0xffff),
REG_CLKDIV);
spin_unlock_irqrestore(&i2c->lock, flags);

...if we really end up with on a system with a dynamically changing
clock that uses the new-style timing and we see real problems, we can
always try to come up with a way to avoid any problems. Sound OK?

Otherwise, I think things look good to me. Caesar's comments would
also be good to fix.

-Doug