linux-kernel - Re: [PATCH v2 2/2] reset: Reset controller driver for Intel LGM SoC

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Date:   Tue, 8 Oct 2019 10:47:03 +0800
From:   Dilip Kota <eswara.kota@...ux.intel.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Philipp Zabel <pza@...gutronix.de>
Cc:     "Chuan Hua, Lei" <chuanhua.lei@...ux.intel.com>,
        cheol.yong.kim@...el.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, qi-ming.wu@...el.com,
        robh@...nel.org, Hauke Mehrtens <hauke@...ke-m.de>
Subject: Re: [PATCH v2 2/2] reset: Reset controller driver for Intel LGM SoC

Hi Martin,Philipp,

On 10/8/2019 3:53 AM, Martin Blumenstingl wrote:
> Hi Philipp,
>
> On Thu, Oct 3, 2019 at 4:19 PM Philipp Zabel <pza@...gutronix.de> wrote:
> [...]
>>> because the register layout was greatly simplified for the newer SoCs
>>> (for which there is reset-intel) compared to the older ones
>>> (reset-lantiq).
>>> Dilip's suggestion (in my own words) is that you take his new
>>> reset-intel driver, then we will work on porting reset-lantiq over to
>>> that so in the end we can drop the reset-lantiq driver.
>> Just to be sure, you are suggesting to add support for the current
>> lantiq,reset binding to the reset-intel driver at a later point? I
>> see no reason not to do that, but I'm also not quite sure what the
>> benefit will be over just keeping reset-lantiq as is?
> according to Chuan and Dilip the current reset-lantiq implementation
> is wrong [0].
> my understanding is that the Lantiq and Intel LGM reset controllers
> are identical except:
> - the Lantiq variant uses a weird register layout (reset and status
> registers not at consecutive offsets)
> - the bits of the reset and status registers sometimes don't match on
> the Lantiq variant
> - the Intel variant has a dedicated registers area for the reset
> controller registers, while the Lantiq variant mixes them with various
> other functionality (for example: USB2 PHYs)
>
>>> This approach means more work for me (as I am probably the one who
>>> then has to do the work to port reset-lantiq over to reset-intel).
>> More work than what alternative?
> compared to "fixing" the existing reset-lantiq driver (reset callback)
> and then (instead of adding a new driver) integrating Intel LGM
> support into reset-lantiq

Integrating Intel LGM support into reset-lantiq boils down to re-writing 
reset-lantiq driver as intel-reset driver and adding Lantiq variant 
support. Why because reset-lantiq driver is not according to hardware 
design[1].

I see the final best solution is to integrate Lantiq variant driver to 
intel-reset driver.[1]
I hope you guys are ok with it. Please let me know your view.


Regards,
Dilip

[1]: https://www.spinics.net/lists/devicetree/msg308930.html

>
>>> I'm happy to do that work if you think that it's worth following this
>>> approach.  So I want your opinion on this before I spend any effort on
>>> porting reset-lantiq over to reset-intel.
>> Reset drivers are typically so simple, I'm not quite sure whether it is
>> worth to integrate multiple drivers if it complicates matters too much.
>> In this case though I expect it would just be adding support for a
>> custom .of_xlate and lantiq specific register property parsing?
> yes, that's how I understand the Lantiq and Intel reset controllers:
> - reset/status/assert/deassert callbacks would be shared across all variants
> - register parsing and of_xlate are SoC specific
>
>
> Martin
>
>
> [0] https://www.spinics.net/lists/devicetree/msg305951.html