[U-Boot] Fixed clock driver (clk: convert API to match reset/mailbox style)

[Simon Glass]

Hi Michal,

On 16 November 2016 at 00:15, Michal Simek <michal.simek at xilinx.com> wrote:
> Hi Simon,
>
> On 15.11.2016 20:23, Simon Glass wrote:
>> Hi Michal,
>>
>> On 15 November 2016 at 12:07, Michal Simek <monstr at monstr.eu> wrote:
>>> Hi guys,
>>>
>>> I just found today with playing with clock drivers that the patch
>>> clk: convert API to match reset/mailbox style
>>> (sha1: 135aa95002646c46e89de93fa36adad1b010548f)
>>>
>>> added this part of code to fixed clock driver
>>> -static ulong clk_fixed_rate_get_rate(struct udevice *dev)
>>> +static ulong clk_fixed_rate_get_rate(struct clk *clk)
>>>  {
>>> -       return to_clk_fixed_rate(dev)->fixed_rate;
>>> -}
>>> +       if (clk->id != 0)
>>> +               return -EINVAL;
>>>
>>>
>>> which is returning -EINVAL when ulong should be returned.
>>
>> This is intended - you can use IS_ERR_VALUE() to check if it is an error.
>
> ok then some drivers needs to be fixed.
>
> drivers/mmc/atmel_sdhci.c:90:   ret = clk_set_rate(&clk, gck_rate);
> drivers/mmc/atmel_sdhci.c-91-   if (ret)
> drivers/mmc/atmel_sdhci.c-92-           return ret;
>
>
> drivers/mmc/msm_sdhci.c:79:     ret = clk_set_rate(&clk, clk_rate);
> drivers/mmc/msm_sdhci.c-80-     clk_free(&clk);
> drivers/mmc/msm_sdhci.c-81-     if (ret < 0)
>
> drivers/net/dwc_eth_qos.c:484:  ret = clk_set_rate(&eqos->clk_ptp_ref,
> 125 * 1000 * 1000);
> drivers/net/dwc_eth_qos.c-485-  if (ret < 0) {
> drivers/net/dwc_eth_qos.c:486:          error("clk_set_rate(clk_ptp_ref)
> failed: %d", ret);
> drivers/net/dwc_eth_qos.c-487-          goto err_disable_clk_ptp_ref;
> drivers/net/dwc_eth_qos.c-488-  }
>
> drivers/serial/serial_msm.c:175:        ret = clk_set_rate(&clk, clk_rate);
> drivers/serial/serial_msm.c-176-        clk_free(&clk);
> drivers/serial/serial_msm.c-177-        if (ret < 0)
>
> drivers/spi/rk_spi.c:176:       ret = clk_set_rate(&priv->clk, 99000000);
> drivers/spi/rk_spi.c-177-       if (ret < 0) {
> drivers/spi/rk_spi.c-178-               debug("%s: Failed to set clock:
> %d\n", __func__, ret);

Yes indeed.

>
>
>>
>>>
>>> The next thing I have found is that fixed clock driver has no set_rate
>>> function which is fine but when I was testing one driver which tries to
>>> set rate then error code was generated but without any useful
>>> information what happened.
>>
>> It should return -ENOSYS, right?
>
> I think -EINVAL in driver as reaction for incorrect id looks good.
> It was more about returning minus value where you should return unsigned.

Yes that's right. I meant -ENOSYS when the driver does not implement the method.

But consider -ENOENT when there is no such thing, as we tend to use
-EINVAL for invalid data (e.g. in device tree)

>
>>
>>> Are you ok with adding empty set_rate function with returning error
>>> message that set rate is not supported for fixed clocks?
>>
>> What would it return that is different? If you are asking for a
>> printed error message, that would bloat the code. So long as the
>> caller checks the error we should be OK.
>
> Caller checks the return code for sure but it is a question if this is
> enough for people to know what's wrong. When this happen you have no
> clue that this problem is coming from clock subsystem.
> I can add one print message to the driver but the same message will end
> up in all these drivers.

IMO a nice solution to this sort of thing is to improve U-Boot's debug
facilities, so you can turn on debugging without having to add #define
DEBUG in each file. The problem is that you bloat the code for a case
that (once development is done) never happens. In particular a great
feature would be something that prints out an error trace, showing
where the error is created. E.g.

#ifdef GLOBAL_DEBUG
#define ERR_RET(val)  ({ printf("%s: %d: Returning error %d\n",
__func__, _LINE__, val); return (val); }, ret)
#else
#define ERR_RET(val) (val)
#endif

Then:

if (ret)
   return ERR_RET(ret)

If we start adding printf() to drivers we carry that load into
production code. I think it is easy to print the error in the board
and then you can start digging.

Regards,
Simon