linux-kernel - Re: [PATCH 2/5] platform: arm64: add Huawei Matebook E Go (sc8280xp) EC driver

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Message-ID: <uqr2hibbl4krkseeal6shmcifctrppimk4tr3y4i64luqpslsq@q3mz2ppencwl>
Date: Fri, 3 Jan 2025 07:38:48 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Pengyu Luo <mitltlatltl@...il.com>
Cc: quic_aiquny@...cinc.com, andersson@...nel.org, 
	bryan.odonoghue@...aro.org, conor+dt@...nel.org, devicetree@...r.kernel.org, 
	gregkh@...uxfoundation.org, hdegoede@...hat.com, heikki.krogerus@...ux.intel.com, 
	ilpo.jarvinen@...ux.intel.com, konradybcio@...nel.org, krzk+dt@...nel.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	linux-usb@...r.kernel.org, nikita@...n.ru, platform-driver-x86@...r.kernel.org, 
	robh@...nel.org, sre@...nel.org
Subject: Re: [PATCH 2/5] platform: arm64: add Huawei Matebook E Go (sc8280xp)
 EC driver

On Tue, Dec 31, 2024 at 03:44:36PM +0800, Pengyu Luo wrote:
> On Tue, Dec 31, 2024 at 1:00 PM Aiqun(Maria) Yu <quic_aiquny@...cinc.com> wrote:
> > On 12/30/2024 6:44 PM, Pengyu Luo wrote:
> > > On Mon, Dec 30, 2024 at 5:04 PM Aiqun(Maria) Yu <quic_aiquny@...cinc.com> wrote:
> > >> On 12/28/2024 1:13 AM, Pengyu Luo wrote:
> > [...]
> > >>> +     i2c_transfer(client->adapter, msgs, 2);
> > >>
> > >> ARRAY_SIZE(msgs) is suggested instead of pure 2.
> > >>
> > >
> > > Agree
> > >
> > >>> +     usleep_range(2000, 2500);
> > >>
> > >> Why is a sleep needed here? Is this information specified in any datasheet?
> > >>
> > >
> > > Have a break between 2 transaction. This sleep happens in acpi code, also
> > > inside a critical region. I rearranged it.
> > >
> > > Local7 = Acquire (\_SB.IC16.MUEC, 0x03E8)
> > > ...
> > > write ops
> > > ...
> > > Sleep (0x02)
> > > ...
> > > read ops
> > > ...
> > > Release (\_SB.IC16.MUEC)
> >
> > Could you please share the exact code snippet that is being referenced?
> > I'm a bit confused because it doesn't seem to align with the current
> > logic, which doesn't have read operations within the same mutex lock. I
> > also want to understand the background and necessity of the sleep function.
> >
> 
> I mentioned I rearranged it to optimize it. In a EC transaction,
> write sleep read => write read sleep, in this way, we sleep once a
> transaction.

Sleeping between write and read is logical: it provides EC some time to
respond. Sleeping after read is complete doesn't seem to have any
reason.

> 
> Please search
> 'device name + acpi table' on the internet, someone dumped it and uploaded
> it, in SSDT, check ECCD. I am not sure if huawei allows users to dump it.
> So I don't provide it here.

-- 
With best wishes
Dmitry