linux-kernel - Re: [PATCH 1/3] i2c: aspeed: avoid new registers definition of AST2600

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Message-ID: <20210524015310.GA2591@aspeedtech.com>
Date:   Mon, 24 May 2021 09:53:11 +0800
From:   Jamin Lin <jamin_lin@...eedtech.com>
To:     Tao Ren <rentao.bupt@...il.com>
CC:     Joel Stanley <joel@....id.au>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:ARM/ASPEED MACHINE SUPPORT" 
        <linux-aspeed@...ts.ozlabs.org>,
        "moderated list:ARM/ASPEED I2C DRIVER" <openbmc@...ts.ozlabs.org>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        Rayn Chen <rayn_chen@...eedtech.com>,
        "open list:I2C SUBSYSTEM HOST DRIVERS" <linux-i2c@...r.kernel.org>,
        Steven Lee <steven_lee@...eedtech.com>,
        "moderated list:ARM/ASPEED MACHINE SUPPORT" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/3] i2c: aspeed: avoid new registers definition of
 AST2600

The 05/21/2021 02:00, Tao Ren wrote:
> Hi Jamin,
> 
> On Thu, May 20, 2021 at 11:31:41AM +0800, Jamin Lin wrote:
> > The 05/19/2021 22:59, Joel Stanley wrote:
> > > On Wed, 19 May 2021 at 08:05, Jamin Lin <jamin_lin@...eedtech.com> wrote:
> > > >
> > > > The register definition between AST2600 A2 and A3 is different.
> > > > This patch avoid new registers definition of AST2600 to use
> > > > this driver. We will submit the path for the new registers
> > > > definition of AST2600.
> > > 
> > > The AST2600 v9 datasheet says that bit 2 selects between old and new
> > > register sets, and that the old register set is the default.
> > > 
> > > Has the default changed for the A3?, and the datasheet is incorrect?
> > > 
> > > Does the A3 still support the old register set?
> > > 
> > We suggest user to use the new i2c driver for AST2600 and we will sumbit
> > it. This driver is used to AST2500 and AST2400 SOCs. Change this
> > driver to check global register of i2c to avoid user build the wrong driver. 
> 
> If I understand correctly, the answer implies old register set is still
> supported in A3 although aspeed suggest people using the new driver/mode?
> 
> Can you please share more context behind the suggestion? Such as new
> register mode has better performance? Or some known issues that were
> deteted in old mode are fixed in new register mode?
>
Yes, AST2600 A1, A2 and A3 support both old and new register set. The difference
between old and new register set are the register address and supported registers.
User can choose to use both old and new register set. However, ASPEED would like to 
change new register set by default for AST2600.
Thanks-Jamin
> 
> Cheers,
> 
> Tao