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

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Date:   Thu, 3 Oct 2019 16:19:55 +0200
From:   Philipp Zabel <pza@...gutronix.de>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     Dilip Kota <eswara.kota@...ux.intel.com>,
        "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, Dilip,

On Thu, Sep 19, 2019 at 09:51:48PM +0200, Martin Blumenstingl wrote:
> Hi Dilip,
> 
> (sorry for the late reply)

Same, sorry for the delay.

> On Thu, Sep 12, 2019 at 8:38 AM Dilip Kota <eswara.kota@...ux.intel.com> wrote:
> [...]
> > The major difference between the vrx200 and lgm is:
> > 1.) RCU in vrx200 is having multiple register regions wheres RCU in lgm
> > has one single register region.
> > 2.) Register offsets and bit offsets are different.
> >
> > So enhancing the intel-reset-syscon.c to provide compatibility/support
> > for vrx200.
> > Please check the below dtsi binding proposal and let me know your view.
> >
> > rcu0:reset-controller@...00000 {
> >      compatible= "intel,rcu-lgm";
> >      reg = <0x0000000 0x80000>, <reg_set2 size>, <reg_set3 size>,
> > <reg_set4 size>;
> I'm not sure that I understand what are reg_set2/3/4 for
> the first resource (0x80000 at 0x0) already covers the whole LGM RCU,
> so what is the purpose of the other register resources
> 
> >     intel,global-reset = <0x10 30>;
> >     #reset-cells = <3>;
> > };
> >
> > "#reset-cells":
> >    const:3
> >    description: |
> >      The 1st cell is the reset register offset.
> >      The 2nd cell is the reset set bit offset.
> >      The 3rd cell is the reset status bit offset.
> I think this will work fine for VRX200 (and even older SoCs)
> as you have described in your previous emails we can determine the
> status offset from the reset offset using a simple if/else
> 
> for LGM I like your initial suggestion with #reset-cells = <2> because
> it's easier to read and write.
>
> > Reset driver takes care of parsing the register address "reg" as per the
> > ".data" structure in struct of_device_id.
> > Reset driver takes care of traversing the status register offset.
> the differentiation between two and three #reset-cells can also happen
> based on the struct of_device_id:
> - the LGM implementation would simply also use the reset bit as status
> bit (only two cells are needed)
> - the implementation for earlier SoCs would parse the third cell and
> use that as status bit
> 
> Philipp, can you please share your opinion on how to move forward with
> the reset-intel driver from this series?

That all sounds reasonable for VRX200/LGM to me.

> 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?

> 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?

> 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?

regards
Philipp