Re: [PATCH v2 2/2] phy: qualcomm: phy-qcom-eusb2-repeater: rework reg override handler

From: Pengyu Luo <mitltlatltl@gmail.com>
To: dmitry.baryshkov@oss.qualcomm.com
Cc: abel.vesa@linaro.org, conor+dt@kernel.org,
	devicetree@vger.kernel.org, kishon@kernel.org,
	krzk+dt@kernel.org, linux-arm-msm@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-phy@lists.infradead.org,
	mitltlatltl@gmail.com, robh@kernel.org, sfr@canb.auug.org.au,
	vkoul@kernel.org
Subject: Re: [PATCH v2 2/2] phy: qualcomm: phy-qcom-eusb2-repeater: rework reg override handler
Date: Tue, 29 Apr 2025 17:23:29 +0800	[thread overview]
Message-ID: <20250429092331.53054-1-mitltlatltl@gmail.com> (raw)
In-Reply-To: <n5z5atbxkwqllni6cgygcw5nn7z4w3yjznhpkaajw6tggenxb3@kxpk2e6vmvlj>

On Tue, Apr 29, 2025 at 12:58 AM Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> wrote:
> On Sat, Apr 26, 2025 at 04:14:23PM +0800, Pengyu Luo wrote:
> > On Sat, Apr 26, 2025 at 3:41 AM Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> wrote:
> > > On Wed, Apr 16, 2025 at 08:02:01PM +0800, Pengyu Luo wrote:
> > > > In downstream tree, many registers need to be overridden, it varies
> > > > from devices and platforms, with these registers getting more, adding
> > > > a handler for this is helpful.
> > >
> > > It should be noted that previously all values were applied during _init
> > > phase, before checking the status etc. Now the overrides are programmed
> > > from the set_mode. Should you still program sane defaults at the init
> > > stage too?
> > >
> >
> > I think programming in set_mode is ok. When we init(dwc3_core_init), we
> > set_mode(dwc3_core_init_mode) later, please check
> > https://elixir.bootlin.com/linux/v6.14.3/source/drivers/usb/dwc3/core.c#L2287
>
> Yes, but that happens after reading status regs, etc.
>
> > Actually, in the downstream, all the things are done in init, it
> > overrides first, then masked write the deaults, finally it set_mode,
> > you can check here
> > https://github.com/OnePlusOSS/android_kernel_oneplus_sm8650/blob/oneplus/sm8650_v_15.0.0_pad_pro/drivers/usb/repeater/repeater-qti-pmic-eusb2.c#L356
>
> I'd stick to this approach too. Program everything in init, then
> program mode-dependent regs in set_mode.
>

If so, I don't mind programming the defaults in init, then programming
overrides in set_mode.

> >
> > > BTW, is there a real need to override those for the platform you are
> > > working on? Could you please provide some details, maybe in the cover
> > > letter.
> >
> > I am not quite sure, recently, I expirenced mode switching failure,
> > when I `echo device > /sys/kernel/debug/usb/a600000.usb/mode`, Ethernet
> > Gadget wouldn't work again, my desktop can't connect to it.
>
> Do you have at least a list of the properties / registers that
> downstream programs on your platform? I mean, it's not infrequent that
> vendor kernel is more versatile than necessary, as it is being used
> during bringup / etc. I'd suggest to limit supported overrides to those
> necessary for your platform (and add a comment that there were other
> available).
>

Yes, I only added the necessary overrides(0x54, and mode handling).
Please check

https://github.com/OnePlusOSS/android_kernel_modules_and_devicetree_oneplus_sm8650/blob/oneplus/sm8650_v_15.0.0_pad_pro/kernel_platform/qcom/proprietary/devicetree/oplus/oplus_misc/oplus-misc-23926.dtsi#L26

Best wishes,
Pengyu