Hi Russell,
On 12/17/2014 06:40 PM, Russell King - ARM Linux wrote:
> On Wed, Dec 17, 2014 at 05:44:33PM +0800, Liu Ying wrote:
>> Hi Thierry,
>>
>> Sorry for the late response.
>> I tried to address almost all your comments locally first.
>> More feedback below.
>>
>> On 12/10/2014 09:16 PM, Thierry Reding wrote:
>>> On Wed, Dec 10, 2014 at 04:37:22PM +0800, Liu Ying wrote:
>>>> +static int check_status(struct imx_mipi_dsi *dsi, u32 reg, u32 status,
>>>> + int timeout, bool to_set)
>>>> +{
>>>> + u32 val;
>>>> + bool out = false;
>>>> +
>>>> + val = dsi_read(dsi, reg);
>>>> + for (;;) {
>>>> + out = to_set ? (val & status) : !(val & status);
>>>> + if (out)
>>>> + break;
>>>> +
>>>> + if (!timeout--)
>>>> + return -EFAULT;
>>>> +
>>>> + msleep(1);
>>>> + val = dsi_read(dsi, reg);
>>>> + }
>>>> + return 0;
>>>> +}
>>>
>>> You should probably use a properly timed loop here. msleep() isn't
>>> guaranteed to return after exactly one millisecond, so your timeout is
>>> never going to be accurate. Something like the following would be better
>>> in my opinion:
>>>
>>> timeout = jiffies + msecs_to_jiffies(timeout);
>>>
>>> while (time_before(jiffies, timeout)) {
>>> ...
>>> }
>>>
>>> Also timeout should be unsigned long in that case.
>>
>> Accepted.
>
> Actually, that's a bad example: what we want to do is to assess success
> after we wait, before we decide that something has failed. In other
> words, we don't want to wait, and decide that we failed without first
> checking for success.
>
> In any case, returning -EFAULT is not sane: EFAULT doesn't mean "fault"
> it means "Bad address", and it is returned to userspace to mean that
> userspace passed the kernel a bad address. That definition does /not/
> fit what's going on here.
>
> timeout = jiffies + msecs_to_jiffies(timeout);
>
> do {
> val = dsi_read(dsi, reg);
> out = to_set ? (val & status) : !(val & status);
> if (out)
> break;
>
> if (time_is_after_jiffies(timeout))
time_is_after_jiffies(a) is defined as time_before(jiffies, a).
So, this line should be changed to
if (time_after(jiffies, timeout))
Right?
> return -ETIMEDOUT;
>
> msleep(1);
> } while (1);
>
> return 0;
>
> would be better: we only fail immediately after we have checked whether
> we succeeded, and we also do the first check immediately.
>
Does this one look better? I use cpu_relax() instead of msleep(1).
expire = jiffies + msecs_to_jiffies(timeout);
for (;;) {
val = dsi_read(dsi, reg);
out = to_set ? (val & status) : !(val & status);
if (out)
break;
if (time_after(jiffies, expire))
return -ETIMEDOUT;
cpu_relax();
}
return 0;
Regards,
Liu Ying
