Message-ID: <d5d0bbdbfdce06a6e2ad34f2fa8f27d4eaf36207.camel@codeconstruct.com.au>
Subject: Re: [PATCH v5 1/2] dt-bindings: i2c: Add support for ASPEED i2Cv2
From:   Jeremy Kerr <jk@codeconstruct.com.au>
To:     Ryan Chen <ryan_chen@aspeedtech.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Joel Stanley <joel@jms.id.au>,
        Andrew Jeffery <andrew@aj.id.au>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        "openbmc@lists.ozlabs.org" <openbmc@lists.ozlabs.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-aspeed@lists.ozlabs.org" <linux-aspeed@lists.ozlabs.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Date:   Wed, 22 Feb 2023 09:30:14 +0800
In-Reply-To: <TYZPR06MB527469EBE6A18B897D2C1F6CF2A59@TYZPR06MB5274.apcprd06.prod.outlook.com>
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         <20230220061745.1973981-2-ryan_chen@aspeedtech.com>
         <2141e513acc750bf26775f5b435f4dccd41244aa.camel@codeconstruct.com.au>
         <TYZPR06MB5274714E58C319B4FE3B6E1BF2A49@TYZPR06MB5274.apcprd06.prod.outlook.com>
         <dfc2c2c442af55f64e147c920585cb7e6a74939f.camel@codeconstruct.com.au>
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Hi Ryan,

> > On the other hand, if it's just because of OS behaviour, then this
> > doesn't belong
> > in the DT.
> >=20
> > Maybe to help us understand: why would you ever *not* want DMA
> > mode?
> > Isn't that always preferable?
> In AST SOC i2c design is 16 i2c bus share one dma engine.=20

Does this mean that only one i2c controller in the system can be
configured to use DMA? Or is it able to be shared between multiple
controllers?

> It can be switch setting by dts setting. Otherwise driver by default
> probe is DMA mode.

You've explained what the modes do, and how they're switched, and what
the default is. However this doesn't explain *why* someone would want
to choose a particular mode when creating a controller node.

Still with the question above: assuming there are no restrictions on
DMA usage, why wouldn't a driver implementation just enable it always?

Cheers,


Jeremy