linux-kernel - Re: [PATCH v6 1/2] dt-bindings: i2c: aspeed: support for AST2600-i2cv2

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 27 Feb 2023 13:40:12 +0800
From:   Jeremy Kerr <jk@...econstruct.com.au>
To:     Ryan Chen <ryan_chen@...eedtech.com>,
        Andrew Jeffery <andrew@...id.au>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Joel Stanley <joel@....id.au>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 1/2] dt-bindings: i2c: aspeed: support for
 AST2600-i2cv2

Hi Ryan,

> Yes, I2C controller share the same dma engine. The original thought
> can be enable in all i2c channel. But in AST2600 have ERRATA "I2C DMA
> fails when DRAM bus is busy and it can not take DMA write data
> immediately", So it means only 1 i2c bus can be enable for DMA mode.

OK, this is a pretty important detail! I'd suggest putting it in the
binding document.

Anything in the cover letter will get lost after review. If there is
documentation that would be useful for a DTS author, I'd suggest putting
it in the binding.

> It means only 1 bus channel can be enable DMA for use case.
> That following example for board-specific selection.
> It is description in cover-letter.
> The following is board-specific design example.
> Board A                                         Board B
> -------------------------                       ------------------------
> > i2c bus#1(master/slave)  <===fingerprint ===> i2c bus#x (master/slave)|
> > i2c bus#2(master)-> tmp i2c device |        |                   |
> > i2c bus#3(master)-> adc i2c device |        |                   |
> -------------------------                       ------------------------
> 
> - in bus#1 situation, you should use DMA mode.
> Because bus#1 have trunk data needed for transfer, it can enable bus
> dma mode to reduce cpu utilized.

What is "trunk data" in this context? Is this just a statement about the
amount of expected transfers?

> - in bus#2/3 situation, you should use buffer/byte mode
> bus#2/3 is small package transmit, it can enable buffer mode or byte
> mode to reduce memory cache flush overhead.
> Buffer mode is better, because byte mode have interrupt
> overhead(interrupt per byte data transmit),
> 
> -But if you more bus#4 that still have trunk data needed for transfer
> (master/slave),
> it also use buffer mode to transmit. Because bus#1 have been use for
> DMA mode.

So, it sounds like:

 - there's no point in using byte mode, as buffer mode provides
   equivalent functionality with fewer drawbacks (ie, less interrupt
   load)

 - this just leaves the dma and buffer modes

 - only one controller can use dma mode

So: how about just a single boolean property to indicate "use DMA on
this controller"? Something like aspeed,enable-dma? Or if DT binding
experts can suggest something common that might be more suitable?

Cheers,


Jeremy