linux-kernel - Re: [PATCH] usb: phy: add dedicated notifier for charger events

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Date:   Mon, 14 Nov 2022 18:46:06 +0200
From:   Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     sre@...nel.org, orsonzhai@...il.com, baolin.wang@...ux.alibaba.com,
        zhang.lyra@...il.com, felipe.balbi@...ux.intel.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...nsource.cirrus.com, linux-usb@...r.kernel.org,
        tony@...mide.com
Subject: Re: [PATCH] usb: phy: add dedicated notifier for charger events

Hi,

On 14.11.22 г. 18:14 ч., Greg KH wrote:
> On Mon, Nov 14, 2022 at 02:56:02PM +0200, Ivaylo Dimitrov wrote:
>> usb_phy::notifier is already used by various PHY drivers (including
>> phy_generic) to report VBUS status changes and its usage conflicts with
>> charger current limit changes reporting.
> 
> How exactly does it conflict?
> 

see below

>> Fix that by introducing a second notifier that is dedicated to usb charger
>> notifications. Add usb_charger_XXX_notifier functions. Fix charger drivers
>> that currently (ab)use usb_XXX_notifier() to use the new API.
> 
> Why not just set the notifier type to be a new one instead of adding a
> whole new notifier list?  Or use a real callback?  notifier lists are
> really horrid and should be avoided whenever possible.
> 

Not sure what you mean by "notifier type', but if that is that val 
parameter of atomic_notifier_call_chain(), the way it is used by usb 
charger FW:

https://elixir.bootlin.com/linux/latest/source/drivers/usb/phy/phy.c#L132

is not compatible with:

https://elixir.bootlin.com/linux/latest/source/drivers/usb/phy/phy-generic.c#L185

for example, IIUC.

The former wants to send max current as val, while latter sends event 
type as val. Sure, I may create some kind of hack, like using the MSB to 
denote charger events, but that doesn't feel right.

Or, shall I do something else and fix the usage all over the place? 
Please elaborate.

In regards to callback - I didn't want to come-up with a whole new API, 
but just fix the current one. Also, a single callback will not be enough 
- imagine a case with 2 batteries that have to be charged by a single 
USB port, so 2 separate charger devices, most-probably. We will have to 
keep a list of callback functions somehow. I admit my lack of knowledge, 
but, do we already have such API to use?

>> Fixes: a9081a008f84 ("usb: phy: Add USB charger support")
>>
>> Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
> 
> You can't have a blank line between there, checkpatch.pl should have
> complained.
> 

it didn't:

./scripts/checkpatch.pl 
0001-usb-phy-add-dedicated-notifier-for-charger-events.patch
total: 0 errors, 0 warnings, 90 lines checked

0001-usb-phy-add-dedicated-notifier-for-charger-events.patch has no 
obvious style problems and is ready for submission.

Will fix, if I am to send v2

Thanks,
Ivo

> thanks,
> 
> greg k-h
>