Hi all, and thanks for your response.
You are correct Guenter. We need to address both i2c- and gpio-based
multiplexers. You and Jean suggested the following solution:
I2C Mux: i2c-N-mux-i2c-XX (chan_id M)
GPIO Mux: i2c-N-mux-gpio-XX (chan_id M)
Where XX is the i2c address or the first GPIO pin number. This
ensures unique IDs for both technologies.
Adding a parameter to i2c_add_mux_adapter() (as you and Jean
suggested) would solve the problem. Basically, we pass a unique id
string (e.g. "-i2c-XX" or "-gpio-XX") to the API, which then adds to
the "name" as described above. In cases where a unique id is not
required, we can simply pass NULL to i2c_add_mux_adapter(). Here's an
example of what the new API would look like:
struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
struct device *mux_dev,
void *mux_priv, u32 force_nr, u32 chan_id,
unsigned int class,
int (*select) (struct i2c_adapter *,
void *mux_dev, u32 chan_id),
int (*deselect) (struct i2c_adapter *,
void *mux_dev, u32 chan_id),
const char *explicit_id);
The parameter explicit_id gets used as follows:
if (NULL == explicit_id)
explicit_id = "";
snprintf(priv->adap.name, sizeof(priv->adap.name),
"i2c-%d-mux%s (chan_id %d)", i2c_adapter_id(parent), explicit_id, chan_id);
If it's OK will all parties, I can submit a patch for it (and I'll
make sure to reference Guenter and Jean as the designers). This,
however, is a first for me. I read all the documents about submitting
patches. I was just wondering if I should submit against the current
3.18 development or some other "stable" releases.
Regards,
Martin
Martin Belanger
Sr. Software Engineer
1383 North McDowell Blvd.
Petaluma, CA 94954
M(707) 481-3392
Emartin.belanger@xxxxxxxxxxx
www.cyaninc.com
On Fri, Oct 31, 2014 at 2:17 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> On 10/31/2014 02:03 PM, Wolfram Sang wrote:
>>
>> Hi,
>>
>> On Mon, Oct 27, 2014 at 11:46:01AM -0700, Martin Belanger wrote:
>>>
>>> This is regarding a series of emails between Guenter Roeck and Jean
>>> Delvare titled "Problem with multiple i2c multiplexers on one bus, and
>>> mux bus naming" sent in November 2013. Ref:
>>> http://thread.gmane.org/gmane.linux.drivers.i2c/16980
>>
>>
>> Please CC those people then, too. That helps getting their attention.
>> I've done this now.
>>
>>> I'm having the same problem with multiple PCA954x multiplexers on the
>>> same bus and there is no way to tell them apart just by looking at the
>>> "name" file.
>>>
>>> There was a suggestion to change the name from "i2c-N-mux (chan_id M)"
>>> to "i2c-N-mux-XX (chan_id M)" or even "i2c-N-mux-i2c-XX (chan_id M)",
>>> where XX is the multiplexer's i2c address. That would solve my
>>> problem, but unfortunately it looks like Guenter never submitted the
>>> patch (or maybe it was rejected?).
>>
>>
>> It just dropped off :( But you guys have my attention now, let's fix
>> this issue for 3.19! I am just reading through the old mails and will
>> think about it. Input is welcome.
>>
> I didn't follow up on the issue since it was not an immediate concern,
> and my proposed solution had some problems. If I remember correctly,
> one of the problems was that the multiplexer does not have to be an
> i2c chip. In that case XX would be unknown and/or have to be omitted.
>
> Guenter
>
>
>>> I would like to submit a similar change, but I was thinking of adding
>>> a module parameter so that the change is not the default behavior.
>>> The idea is to preserve backward compatibility for applications that
>>> don't require this fix. For example, modprobe i2c-dev
>>> explicit_mux_id=1 would use i2c-N-mux-i2c-XX (chan_id M), whereas
>>> modprobe i2c-dev would default to the current behavior: i.e. i2c-N-mux
>>> (chan_id M).
>>
>>
>> I don't like the need to set a module parameter to fix a flaw. I do
>> consider changing the ABI to have better strings in "name". But as said,
>> I need to think about it a little more...
>>
>> Thanks,
>>
>> Wolfram
>>
>
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