linux-kernel - RE: [PATCH v3] i2c: tegra: Share same DMA channel for RX and TX

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Date:   Thu, 23 Mar 2023 09:26:00 +0000
From:   Akhil R <akhilrajeev@...dia.com>
To:     Jonathan Hunter <jonathanh@...dia.com>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "digetx@...il.com" <digetx@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "wsa@...nel.org" <wsa@...nel.org>
Subject: RE: [PATCH v3] i2c: tegra: Share same DMA channel for RX and TX

> On 22/03/2023 12:00, Akhil R wrote:
> >> On 22/03/2023 10:24, Akhil R wrote:
> >>> Allocate only one DMA channel for I2C and share it for both TX and RX
> >>> instead of using two different DMA hardware channels with the same
> >>> slave ID. Since I2C supports only half duplex, there is no impact on
> >>> perf with this.
> >>>
> >>> Signed-off-by: Akhil R <akhilrajeev@...dia.com>
> >>
> >> Just to confirm. This impacts all Tegra devices from Tegra20 to the
> >> latest. Does this work for all Tegra and the different DMA controllers
> >> that they have?
> >>
> > Yes, It should. I could see in the APB DMA driver that the same channel
> > could be used for TX and RX and the direction is configured only during
> > dma_prep_*() calls.
> > I did not test it on a Tegra with APB DMA, but since it works very similar
> > to GPC DMA there should not be any impact.
> 
> 
> OK. BTW, this does not apply cleanly on top of -next. It appears that
> this is based on top "i2c: tegra: Fix PEC support for SMBUS block read"
> and that one needs to be applied first. This can be avoided if you send
> as a series.
> 
Oh. Okay. I used 'git am --3way' when I tried, and the conflict went unnoticed.
Shall I send a new version on top of -next?
The two patches were added in different contexts and that’s why I did not
combine them as a series.

Regards,
Akhil