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Subject: Re: [PATCH v5] serial: samsung: use dma_ops of DMA if attached
To:     Tamseel Shams <m.shams@samsung.com>, gregkh@linuxfoundation.org,
        jirislaby@kernel.org
Cc:     linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, linux-serial@vger.kernel.org,
        linux-kernel@vger.kernel.org, alim.akhtar@samsung.com,
        ajaykumar.rs@samsung.com, robin.murphy@arm.com
References: <CGME20210629045610epcas5p4fa9d2a217b351a950899073d6b7d3dfd@epcas5p4.samsung.com>
 <20210629045902.48912-1-m.shams@samsung.com>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Message-ID: <8569ce54-26ef-e36a-b3a9-2d31e2575bd2@canonical.com>
Date:   Tue, 29 Jun 2021 11:44:51 +0200
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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@samsung.com>
> Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.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@canonical.com>


Best regards,
Krzysztof