linux-kernel - Re: [PATCH 2/4] soc: aspeed: Add UART DMA support

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Message-ID: <ad200b06-368a-1f01-41e1-6b639d128186@linaro.org>
Date:   Mon, 13 Feb 2023 09:31:30 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     ChiaWei Wang <chiawei_wang@...eedtech.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.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>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>
Subject: Re: [PATCH 2/4] soc: aspeed: Add UART DMA support

On 13/02/2023 02:50, ChiaWei Wang wrote:
>> From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> Sent: Friday, February 10, 2023 5:14 PM
>>
>> On 10/02/2023 08:26, Chia-Wei Wang wrote:
>>> This driver provides DMA support for AST26xx UART and VUART devices.
>>> It is useful to offload CPU overhead while using UART/VUART for binary
>>> file transfer.
>>>
>>> Signed-off-by: Chia-Wei Wang <chiawei_wang@...eedtech.com>
>>> ---
>>>  drivers/soc/aspeed/Kconfig             |   9 +
>>>  drivers/soc/aspeed/Makefile            |   1 +
>>>  drivers/soc/aspeed/aspeed-udma.c       | 447
>> +++++++++++++++++++++++++
>>>  include/linux/soc/aspeed/aspeed-udma.h |  34 ++
>>
>> NAK.
>>
>> DMA drivers do not go to soc, but to dma subsystem.
> 
> The UDMA is dedicated only to UART use and is not fully fit to the DMAEngine subsystem.
> For example, the suspend/resume operations of common DMA engine are not supported.
> After observing certain existing DMA implementation in other soc folders, we put UDMA in the soc/aspeed as well.
> If it is not appropriate, should we integrate UDMA into the UART driver or try to make UDMA DMAEngine based?


You did not Cc dma folks, so how would I know... Maybe soc is right
place if the DMA driver is not suitable for other consumers than UART.
Maybe not.

Best regards,
Krzysztof