Message-ID: <08f2f5aa-af3c-79c1-2cbb-c4d5eb5dce93@codeaurora.org>
Date:   Tue, 7 Mar 2017 14:56:39 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     robh+dt <robh+dt@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4 2/4] phy: qcom-qusb2: New driver for QUSB2 PHY on Qcom
 chips

Hi,


On 03/07/2017 02:34 PM, Kishon Vijay Abraham I wrote:
> Hi,
>
> On Thursday 02 March 2017 10:10 PM, Vivek Gautam wrote:
>> Hi Kishon,
>>
>>
>> On Wed, Feb 22, 2017 at 9:29 AM, Vivek Gautam
>> <vivek.gautam@...eaurora.org> wrote:
>>> Hi Kishon,
>>>
>>>
>>> On Fri, Jan 27, 2017 at 11:54 AM, Vivek Gautam
>>> <vivek.gautam@...eaurora.org> wrote:
>>>>
>>>> On 01/26/2017 11:45 PM, Bjorn Andersson wrote:
>>>>> On Tue 24 Jan 01:19 PST 2017, Kishon Vijay Abraham I wrote:
>>>>>> On Monday 23 January 2017 03:43 PM, Vivek Gautam wrote:
>>>>>>> On Wed, Jan 18, 2017 at 11:33 PM, Bjorn Andersson
>>>>> [..]
>>>>>>> Yes, that's correct. The QMP and QUSB2 phy init sequences are a bunch
>>>>>>> of static values for a particular IP version. These values hardly give a
>>>>>>> meaningful data to put few phy bindings that could be referenced
>>>>>>> to configure the phy further.
>>>>>> Not really. You can have clearly defined phy binding to give meaningful
>>>>>> data.
>>>>>> Every driver doing the same configuration bloats the driver and these
>>>>>> configuration values are just magic values which hardly can be reviewed
>>>>>> by anyone.
>>>>>>>> Further more moving this blob to devicetree will not allow us to treat
>>>>>>>> the various QMP configurations as one HW block, as there are other
>>>>>>>> differences as well.
>>>>>>>>
>>>>>>>> Like many other drivers it's possible to create a generic version that
>>>>>>>> has every bit of logic driven by configuration from devicetree, but
>>>>>>>> like
>>>>>>>> most of those cases this is not the way we split things.
>>>>>>>>
>>>>>>>> And this has the side effect of keeping the dts files human readable,
>>>>>>>> human understandable and human maintainable.
>>>>>> right. That's why I recommend having clearly defined bindings.
>>>>>>          phy,tx-<param1> = <val, offset, mask>
>>>>>>          phy,tx-<param2> = <val, offset, mask>
>>>>>>          phy,tx-<param3> = <val, offset, mask>
>>>>> There's no doubt that this table needs to be encoded somewhere, so the
>>>>> question is should we hard code this in a C file or in a DTSI file.
>>>>>
>>>>> Skimming through [1] I see examples of things that differs based on how
>>>>> the specific component is integrated in a SoC or on a particular board -
>>>>> properties that are relevant to a "system integrator".
>>>>>
>>>>> As far as I can tell this blob will, if ever, only be changed by a
>>>>> driver developer and as such it's not carry information about how this
>>>>> component relates to the rest of the system and should as such not be
>>>>> part of the device tree.
>>>>>
>>>>>
>>>>> If there are properties of the hardware that is affected by how the
>>>>> component is integrated in the system I really would like for those to
>>>>> be exposed as human-readable properties that I can understand and alter
>>>>> without deep knowledge about the register map of the hardware block.
>>>>
>>>> I am reaching out to our internal teams to get more information
>>>> on different possible phy configurations, based on which the registers
>>>> values are decided.
>>>> This is something that i tried to understand in the past as well, but
>>>> couldn't
>>>> grab much information that time.
>>>> Will come back with relevant information on this.
>>>>
>>> We have started looking into understanding the PHYs on msm and
>>> eventually create a set of generic phy bindings that can serve multiple
>>> platforms.
>>> But this task, I presume, will take its course and will involve multi-party
>>> discussions.
>>>
>>> For these QUSB2 and QMP phy drivers, a good amount of work has
>>> already gone in getting these drivers in upstream state.
>>> The common QMP phy driver supports a bunch of controllers on msm
>>> platforms - USB, PCIe and UFS and there are platforms such as DB820c
>>> and others that want to pull in these changes from upstream.
>>> The future phy controllers also depend on these drivers and we don't want
>>> to hold other developers to contribute to these drivers.
>>> So, we wish to not delay these drivers further because of the phy bindings.
>>> I see that there are phys that still program the registers-value pairs for
>>> phy initialization.
>>>
>>> We will keep working on the bindings while these patches
>>> make way to upstream.
>>>
>>> Can you consider pulling in these drivers?
>>> I can send the next version of these drivers with other comments addressed.
>>> Please let me know your comments.
>> Gentle ping. Any thoughts on this ?
> sure, lets hold the phy configuration binding and complete the rest of the patch.

Sure, thanks. Will post out the next version of patches soon.

Regards
Vivek

>
> Thanks
> Kishon

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