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

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Date:   Mon, 13 Feb 2023 01:50:07 +0000
From:   ChiaWei Wang <chiawei_wang@...eedtech.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "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

> 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?

Regards,
Chiawei