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Date:   Wed, 22 Mar 2023 13:42:21 +0000
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Subject: Re: [PATCH v3] i2c: tegra: Share same DMA channel for RX and TX
Content-Language: en-US
To:     Akhil R <akhilrajeev@nvidia.com>,
        "christian.koenig@amd.com" <christian.koenig@amd.com>,
        "digetx@gmail.com" <digetx@gmail.com>,
        Laxman Dewangan <ldewangan@nvidia.com>,
        "linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        "sumit.semwal@linaro.org" <sumit.semwal@linaro.org>,
        "thierry.reding@gmail.com" <thierry.reding@gmail.com>,
        "wsa@kernel.org" <wsa@kernel.org>
References: <20230322102413.52886-1-akhilrajeev@nvidia.com>
 <db870e74-9d97-740a-9829-5fafc0bb0559@nvidia.com>
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From:   Jon Hunter <jonathanh@nvidia.com>
In-Reply-To: <SJ1PR12MB6339FC0B9BB57D1D2300D46CC0869@SJ1PR12MB6339.namprd12.prod.outlook.com>
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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@nvidia.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.

Jon

-- 
nvpublic