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

[David.Wu]

Hi Doug,

å 2016/5/12 1:37, Doug Anderson åé:
> Hi,
>
> On Tue, May 10, 2016 at 12:31 PM, David Wu <david.wu@xxxxxxxxxxxxxx> 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.

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