linux-kernel - Re: [PATCH net-next v2 05/10] drivers: base: Add device_find

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Date:   Thu, 12 Jan 2017 14:50:39 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, jason@...edaemon.net, andrew@...n.ch,
        sebastian.hesselbarth@...il.com,
        gregory.clement@...e-electrons.com, linux@...linux.org.uk,
        vivien.didelot@...oirfairelinux.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH net-next v2 05/10] drivers: base: Add device_find_class()

On 01/12/2017 01:21 PM, David Miller wrote:
> From: Florian Fainelli <f.fainelli@...il.com>
> Date: Wed, 11 Jan 2017 19:41:16 -0800
> 
>> Add a helper function to lookup a device reference given a class name.
>> This is a preliminary patch to remove adhoc code from net/dsa/dsa.c and
>> make it more generic.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>> ---
>>  drivers/base/core.c    | 19 +++++++++++++++++++
>>  include/linux/device.h |  1 +
>>  2 files changed, 20 insertions(+)
>>
>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>> index 020ea7f05520..3dd6047c10d8 100644
>> --- a/drivers/base/core.c
>> +++ b/drivers/base/core.c
>> @@ -2065,6 +2065,25 @@ struct device *device_find_child(struct device *parent, void *data,
>>  }
>>  EXPORT_SYMBOL_GPL(device_find_child);
>>  
>> +static int dev_is_class(struct device *dev, void *class)
> 
> I know you are just moving code, but this class argumnet is a string
> and thus should be "char *" or even "const char *".

Well, this is really so that we don't need to cast the arguments passed
to device_find_child(), which takes a void *data as well. If we made
that a const char *class, we'd get warnings that look like these:

drivers/base/core.c: In function 'device_find_class':
drivers/base/core.c:2083:2: warning: passing argument 2 of
'device_find_child' discards 'const' qualifier from pointer target type
[enabled by default]
  return device_find_child(parent, class, dev_is_class);
  ^
drivers/base/core.c:2050:16: note: expected 'void *' but argument is of
type 'const char *'
 struct device *device_find_child(struct device *parent, void *data,
                ^
drivers/base/core.c:2083:2: warning: passing argument 3 of
'device_find_child' from incompatible pointer type [enabled by default]
  return device_find_child(parent, class, dev_is_class);
  ^
drivers/base/core.c:2050:16: note: expected 'int (*)(struct device *,
void *)' but argument is of type 'int (*)(struct device *, const char *)'
 struct device *device_find_child(struct device *parent, void *data,
                ^

-- 
Florian