Re: [PATCH 5/5] em28xx: fix+improve+unify i2c error handling, debug messages and code comments

["Frank Schäfer" <fschaefer.oss@googlemail.com>]

Am 15.12.2012 14:46, schrieb Antti Palosaari:
> On 12/15/2012 03:01 PM, Frank Schäfer wrote:
>> Am 14.12.2012 18:03, schrieb Antti Palosaari:
>>> On 12/14/2012 06:28 PM, Frank Schäfer wrote:
>>>> - check i2c slave address range (only 7 bit addresses supported)
>>>> - do not pass USB specific error codes to userspace/i2c-subsystem
>>>> - unify the returned error codes and make them compliant with
>>>>     the i2c subsystem spec
>>>> - check number of actually transferred bytes (via USB) everywehere
>>>> - fix/improve debug messages
>>>> - improve code comments
>>>>
>>>> Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
>>>
>>>
>>>> @@ -244,16 +294,20 @@ static int em28xx_i2c_xfer(struct i2c_adapter
>>>> *i2c_adap,
>>>>            dprintk2(2, "%s %s addr=%x len=%d:",
>>>>                 (msgs[i].flags & I2C_M_RD) ? "read" : "write",
>>>>                 i == num - 1 ? "stop" : "nonstop", addr, msgs[i].len);
>>>> +        if (addr > 0xff) {
>>>> +            dprintk2(2, " ERROR: 10 bit addresses not supported\n");
>>>> +            return -EOPNOTSUPP;
>>>> +        }
>>>
>>> There is own flag for 10bit I2C address. Use it (and likely not
>>> compare at all addr validly like that). This kind of address
>>> validation check is quite unnecessary - and after all if it is wanted
>>> then correct place is somewhere in I2C routines.
>>
>> Well, to be 100% sure and strict, we should check both, the flag and the
>> actual address.
>> We support 7 bit addresses only, no matter which i2c algo is used. So
>> doing the address check in each i2c routine seems to be unnecessary code
>> duplication to me ?
>
> I will repeat me, I see it overkill to check address correctness. And
> as I said, that one is general validly could be done easily in I2C
> core - so why the hell you wish make it just only for em28xx ?
>
> I am quite sure if that kind of address validness are saw important
> they are already implemented by I2C core.
>
> Make patch for I2C which does that address validation against client
> 10BIT flag and sent it to the mailing list for discussion.

The I2C core doesn't know about the capabilities of the adapter.
Hence it doesn't know if ten bit addresses will work (the same as with
the message size constraints).
All it does ist to check the client for I2C_CLIENT_TEN && addr > 0x7f
once, when it is instanciated with a call to i2c_new_device().
But we don't use this function in em28xx and the same applies to many
other drivers as well.
Apart from that, the client address and flags can change anytime later
(e.g. when probing devices).

But if you hate the check, I can kick it out.
The risk that it will cause any problems in practice is small.

Regards,
Frank

>
>> BTW: with the em28xx algorithm, the i2c address is transferred as 16 bit
>> value. So 10 bit addresses COULD work in theory... ;)
>
> Could be, but I think 10bit is never used in real life.
>
> regards
> Antti
>