From: Valentin Longchamp <valentin.longchamp@keymile.com>
To: Scott Wood <scottwood@freescale.com>, Wolfram Sang <wsa@the-dreams.de>
Cc: Linux device trees <devicetree@vger.kernel.org>,
danielle.costantino@gmail.com, "Boschung,
Rainer" <Rainer.Boschung@keymile.com>,
"Brunck, Holger" <Holger.Brunck@keymile.com>,
Linux I2C <linux-i2c@vger.kernel.org>,
Linux PowerPC Kernel <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH] i2c-qoriq: modified compatibility for correct prescaler
Date: Tue, 23 Dec 2014 14:23:01 +0100 [thread overview]
Message-ID: <54996CB5.8030808@keymile.com> (raw)
In-Reply-To: <54899FB4.9010207@keymile.com>
Wolfgang, Scott,
On 12/11/2014 02:44 PM, Valentin Longchamp wrote:
> Hi all,
>
> Picking up this issue again.
>
> On 11/26/2014 02:41 AM, Scott Wood wrote:
>> On Tue, 2014-11-25 at 19:13 +0100, Wolfram Sang wrote:
>>> On Mon, Nov 17, 2014 at 07:28:03PM -0600, Scott Wood wrote:
>>>> On Fri, 2014-11-14 at 09:28 +0100, Wolfram Sang wrote:
>>>>>>>
>>>>>>> If we're going to change the device tree I'd rather just add a property
>>>>>>> to say what the prescaler is.
>>>>>>
>>>>>> We would however, leave the boards' device trees that use things like
>>>>>> "fsl,mpc8543-i2c" as is and introduce the prescaler for the others requiring it.
>>>>>>
>>>>>>
>>>>>> Now the drawback is that the driver would require a change, to parse this
>>>>>> prescaler new prescaler property. Would this be OK from your point of view
>>>>>> Wolfram ? If yes, I will send the patches for it.
>>>>>
>>>>> I don't think it is OK.
>>>>
>>>> Why?
>>>
>>> Because I thought it could be deduced. Then, a seperate property would
>>> not be OK.
>>>
>>>>> I'd think it can be deduced from the compatible property.
>>>>
>>>> For almost all existing device trees it cannot be.
>>>
>>> Pity :( If we do introduce a new property, it should probably be
>>> "clock-div". Grepping through binding documentation, that seems
>>> accepted. We should ask DT maintainers, too, to be safe.
>>>
>>>> If you want something that will work without changing device trees,
>>>> you'll need to use SVR to identify the SoC.
>>>
>>> The driver is doing that already, see mpc_i2c_get_sec_cfg_8xxx(). Dunno
>>> if it makes sense to add to it for consistency reasons?
>>
>> That's not SVR, but sure. Better to avoid messing with existing device
>> trees.
>>
>
> What is then the agreement here ? Add a clock-div to the device trees ? Or do
> something similar to mpc_i2c_get_sec_cfg_8xxx() ?
>
> I think the clock-div property is better according to Freescale's AN 2919
> section 3.1 Source clock. All the source clocks are fixed (with a clock-div of 2
> in case of mpc8536/43/45/47/48/67/68/72, plus p2020) except for the mpc8533/44
> where it can be 2 or 3, and that's what mpc_i2c_get_sec_cfg_8xxx() determines.
>
> So mpc_i2c_get_sec_cfg_8xxx() should remain the exception and the other
> prescaler values should be derived from an additional clock-div that must be
> added in the respective device trees (at least for the qoriq devices, because
> for instance mpc8543 already has the correct prescaler thanks to
> mpc_i2c_data_8543 from i2c-mpc.c).
>
Do you have an opinion on the above ?
Valentin
next prev parent reply other threads:[~2014-12-23 13:23 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-17 9:27 [PATCH] i2c-qoriq: modified compatibility for correct prescaler Valentin Longchamp
2014-10-28 23:08 ` Scott Wood
2014-10-29 8:59 ` Valentin Longchamp
2014-11-06 21:58 ` Scott Wood
2014-11-13 0:34 ` Wolfram Sang
2014-11-14 7:43 ` Valentin Longchamp
2014-11-14 8:28 ` Wolfram Sang
2014-11-18 1:28 ` Scott Wood
2014-11-25 18:13 ` Wolfram Sang
2014-11-26 1:41 ` Scott Wood
2014-11-30 4:30 ` Danielle Costantino
2014-12-01 17:23 ` Wolfram Sang
2014-12-11 13:44 ` Valentin Longchamp
2014-12-23 13:23 ` Valentin Longchamp [this message]
2014-12-23 13:49 ` Wolfram Sang
2014-12-27 2:43 ` Scott Wood
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