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: Sat, 26 Apr 2025 16:14:23 +0800	[thread overview]
Message-ID: <20250426081424.422590-1-mitltlatltl@gmail.com> (raw)
In-Reply-To: <q6zqfk3l2khp3tkodxd4pzhufiesyjcypl66zoqzslolwoveyo@ltrw2iulrkqs>

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

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

> 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.

BTW, as you can see in line 356, it is most likely that overrides
related to charging feature. I have not ported charging yet, but adding
more overrides seems harmless, and if overriding, distinguishing which
mode seems necessary, even if some devices use the same sequence. So I
sent the patch.

Best wishes,
Pengyu