linux-kernel - Re: [PATCH 0/3] ARM: davinci: ohci-da8xx: model the vbus GPIO as a fixed regulator

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Date:   Thu, 28 Mar 2019 15:40:08 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
CC:     Kevin Hilman <khilman@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 0/3] ARM: davinci: ohci-da8xx: model the vbus GPIO as a
 fixed regulator

On 27/03/19 6:46 PM, Bartosz Golaszewski wrote:
> śr., 27 mar 2019 o 12:37 Sekhar Nori <nsekhar@...com> napisał(a):
>>
>> Hi Bart,
>>
>> On 26/03/19 9:27 PM, Bartosz Golaszewski wrote:
>>> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
>>>
>>> Adding the vbus GPIO support to the ohci-da8xx driver isn't really the
>>> optimal solution. Rather: it should be modeled as a fixed regulator
>>> in which case the driver already has support.
>>
>> Can you clarify "driver already has support"? You are introducing
>> support to use the VBUS gpio as regulator as part of 3/3.
>>
> 
> The support is there as in: if the driver can obtain the regulator, it
> will enable it. The overcurrent protection does not work however and
> this is what patch 3 adds. Maybe I should rework the ordering in that
> I'd first add the irq thread disabling the regulator if it exists,
> then the regulator fixups to board files and then remove the vbus
> GPIO.
> 
>> I do see other instances of VBUS regulator being used in USB tree. But
>> we just converted the driver to use VBUS and over-current GPIOs in v5.1.
>> So this is a bit of "churn".
>>
> 
> Yes and it's my fault - I simply converted the legacy code without
> giving it enough consideration. I should have used a fixed regulator
> right away, but now it's upstream and we need a follow-up series.
> 
>> Can you document why the current solution is not optimal? Is it to make
>> future device-tree conversion for these boards easier? Or?
>>
> 
> It's sub-optimal from the HW modeling in SW PoV - it is in fact a
> regulator enabled/disabled by a GPIO. Also: it's code duplication as
> currently we check if the vbus GPIO exists and then use it or check if
> the regulator exists and use this as the second choice. The third
> patch actually shrinks the driver.

I see now that the driver supports controlling the VBUS gpio as
regulator already. Something I should have caught in review last time
around.

I agree this patch is an improvement. Lets see what Alan feels.

Also, reg_enabled member of da8xx_ohci_hcd structure seems to be pretty
useless considering regulator API already has use counting. Can you take
a look and remove that too as an added bonus.

Thanks,
Sekhar