linux-kernel - Re: [PATCH v5] serial: samsung: use dma

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Date:   Tue, 29 Jun 2021 11:44:51 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Tamseel Shams <m.shams@...sung.com>, gregkh@...uxfoundation.org,
        jirislaby@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, alim.akhtar@...sung.com,
        ajaykumar.rs@...sung.com, robin.murphy@....com
Subject: Re: [PATCH v5] serial: samsung: use dma_ops of DMA if attached

On 29/06/2021 06:59, Tamseel Shams wrote:
> When DMA is used for TX and RX by serial driver, it should
> pass the DMA device pointer to DMA API instead of UART device
> pointer. DMA device should be used for DMA API because only
> the DMA device is aware of how the device connects to the memory.
> There might be an extra level of address translation due to a
> SMMU attached to the DMA device. When serial device is used for
> DMA API, the DMA API will have no clue of the SMMU attached to
> the DMA device.
> 
> This patch is necessary to fix the SMMU page faults
> which is observed when a DMA(with SMMU enabled) is attached
> to UART for transfer.
> 
> Signed-off-by: Tamseel Shams <m.shams@...sung.com>
> Signed-off-by: Ajay Kumar <ajaykumar.rs@...sung.com>
> ---
> Changes since v1:
> 1. Rebased the patch on "tty-next" branch of TTY driver tree
> 
> Changes since v2:
> 1. Updated the commit message.
> 2. Changed the comment description
> 
> Changes since v3:
> 1. Removed the null pointer check for "dma", "dma->tx_chan" and
> "dma->rx_chan" and instead sending DMA device pointer while calling
> DMA API.
> 
> Changes since v4:
> 1. Fixed the alignments of arguments.
> 
>  drivers/tty/serial/samsung_tty.c | 46 +++++++++++++++++---------------
>  1 file changed, 25 insertions(+), 21 deletions(-)
> 


Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>


Best regards,
Krzysztof