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

David.Wu
2016-05-12T15:07:23Z

Hi Doug，

在 2016/5/12 9:08, David.Wu 写道:
> Hi Doug,
>
> 在 2016/5/12 1:37, Doug Anderson 写道:
>> 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?
>>
>>
>
> Good, add spin_lock is very necessary for atomic write here, thanks for
> your advice.

I also found a subtle bug, it would clean the con register by use
"i2c_writel(i2c, 0, REG_CON)" in rk3x_i2c_stop(). So i think it would be
fixed by using read-modify-write way here in next version.

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