From: vladimir_zapolskiy@mentor•com (Vladimir Zapolskiy)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v3 2/2] drm: bridge/dw_hdmi: add dw hdmi i2c bus adapter support
Date: Thu, 17 Sep 2015 00:16:00 +0300 [thread overview]
Message-ID: <55F9DC10.9020508@mentor.com> (raw)
In-Reply-To: <CAD=FV=XO0cjmmXniGnqvvoWZ=e1EL7t5XDUXVhiNMqWvmaOpMw@mail.gmail.com>
Hi Doug,
On 03.09.2015 02:19, Doug Anderson wrote:
> Russell,
>
> On Wed, Sep 2, 2015 at 4:04 PM, Russell King - ARM Linux
> <linux@arm•linux.org.uk> wrote:
>>>> Also, is it appropriate to hook non-DDC devices to a DDC bus? I suspect
>>>> that's asking for trouble.
>>>
>>> I doubt it's appropriate. Why do you ask?
>>
>> To find out why you want to "specify the I2C bus".
>>
>> Surely if we're talking about the DDC bus, we either want to use a
>> separate I2C bus (in which case the HDMI DT description needs to
>> specify which I2C bus to use) or we want to use the HDMI-internal
>> I2C bus, which being part of the HDMI driver, the HDMI driver will
>> know how to find it itself - there should be no need to put an
>> explicit ddc-i2c-bus self-reference there in that case.
>
> Overall it comes down to bus numbering. Possibly that's a stupid
> reason, but it is my reason nevertheless.
this is a known issue regarding I2C bus numbering.
> Specifically it significantly helps my brain process kernel log
> messages if the i2c bus that's referred to "bus 5" in my SoC's user
> manual shows up consistently as "i2c5" in kernel log messages. It's
> helpful it it shows up as "i2c5" even if "i2c0" - "i2c4" aren't
> enabled.
>
> That's all totally possible by using this type of syntax, like in rk3288.dtsi:
>
> aliases {
> i2c0 = &i2c0;
> i2c1 = &i2c1;
> i2c2 = &i2c2;
> i2c3 = &i2c3;
> i2c4 = &i2c4;
> i2c5 = &i2c5;
>
> Similarly, I'd like "bus 0" to show up as i2c0, which will happen as
> you can see in the above.
>
> The problem is that if another bus registers itself before the SoC's
> i2c0 registers itself and that bus doesn't give a number to itself
> then the i2c subsystem will chose "I2C 0". ...and then when the main
> SoC i2c bus registers itself it will fail because i2c0 is already
> taken.
>
> By having a of_node for the hdmi i2c bus, we can assign a number to it like:
> i2c15 = &hdmi;
>
> This is all described in the two links I referenced in my original reply.
>
>
> A possible other option is to have the i2c subsystem try to start
> numbering at a larger base for all automatically numbered busses
> (those that didn't specify a number). Then it's more likely (though
> still not guaranteed) to conflict with another bus...
Could you please check if commit 03bde7c31a3 serves you?
--
With best wishes,
Vladimir
next prev parent reply other threads:[~2015-09-16 21:16 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-30 21:34 [PATCH v3 2/2] drm: bridge/dw_hdmi: add dw hdmi i2c bus adapter support Vladimir Zapolskiy
2015-08-31 9:22 ` Philipp Zabel
2015-09-02 22:07 ` Doug Anderson
2015-09-02 22:50 ` Russell King - ARM Linux
2015-09-02 23:00 ` Doug Anderson
2015-09-02 23:04 ` Russell King - ARM Linux
2015-09-02 23:19 ` Doug Anderson
2015-09-16 21:16 ` Vladimir Zapolskiy [this message]
2015-09-16 22:02 ` Doug Anderson
2015-09-02 23:43 ` Doug Anderson
2015-09-03 9:19 ` Russell King - ARM Linux
2015-09-03 9:39 ` Thierry Reding
2015-09-03 16:08 ` Doug Anderson
2015-09-08 22:08 ` Wolfram Sang
2015-09-16 20:04 ` Doug Anderson
2015-09-16 20:58 ` Vladimir Zapolskiy
2015-09-16 21:56 ` Doug Anderson
2015-09-16 22:18 ` Russell King - ARM Linux
2015-09-21 14:00 ` Vladimir Zapolskiy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=55F9DC10.9020508@mentor.com \
--to=vladimir_zapolskiy@mentor$(echo .)com \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox