linux-kernel - Re: [PATCH v4 2/4] phy: qcom-qusb2: New driver for QUSB2 PHY on Qcom chips

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Message-ID: <58BE77A1.6090502@ti.com>
Date:   Tue, 7 Mar 2017 14:34:33 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
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 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.

Thanks
Kishon