Re: [PATCH v3 2/3] mmc: usdhi6rol0: add support for UHS modes

[Lars Persson <lars.persson-VrBV9hrLPhE@public.gmane.org>]

On 04/21/2016 09:53 AM, Arnd Bergmann wrote:
> On Thursday 21 April 2016 09:12:52 Lars Persson wrote:
>> On 04/20/2016 04:53 PM, Lars Persson wrote:
>>> Add a start_signal_voltage_switch() operation to support enabling of
>>> UHS modes.
>>>
>>> Signed-off-by: Lars Persson <larper-VrBV9hrLPhE@public.gmane.org>
>>> ---
>>>    drivers/mmc/host/usdhi6rol0.c | 13 +++++++++++++
>>>    1 file changed, 13 insertions(+)
>>>
>>> diff --git a/drivers/mmc/host/usdhi6rol0.c b/drivers/mmc/host/usdhi6rol0.c
>>> index 807c06e..2585ea4 100644
>>> --- a/drivers/mmc/host/usdhi6rol0.c
>>> +++ b/drivers/mmc/host/usdhi6rol0.c
>>> @@ -1147,12 +1147,25 @@ static void usdhi6_enable_sdio_irq(struct mmc_host *mmc, int enable)
>>>        }
>>>    }
>>>
>>> +static int usdhi6_sig_volt_switch(struct mmc_host *mmc, struct mmc_ios *ios)
>>> +{
>>> +     int ret;
>>> +
>>
>> To support boards without regulator we need to put a
>> IS_ERR_OR_NULL(mmc->supply.vqmmc) check here and bail out with return 0.
>> Missing vqmmc is OK according to our binding document, but treated as an
>> error by mmc_regulator_set_vqmmc().
>
> mmc_regulator_set_vqmmc() should already take care of handling
> all the those cases. In general, it's almost always a bug to use
> IS_ERR_OR_NULL(): if you ever feel the need to use it, you should
> either fix the code that made the pointer ambiguous or you have
> misunderstood the interface.
>
> 	Arnd
>

Yes it should of course be IS_ERR() rather than IS_ERR_OR_NULL().

It is a common pattern in all upstream mmc drivers to not make the call 
to mmc_regulator_set_vqmmc() when a regulator is missing. We basically 
want to log errors except for the EINVAL returned in case of a missing 
regulator.


- Lars
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