linux-kernel - Re: [PATCH] i2c: at91: use dma safe buffers

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Message-ID: <fff424e7-247c-38d8-4151-8b0503a16a7d@amd.com>
Date:   Fri, 4 Mar 2022 08:35:44 +0100
From:   Christian König <christian.koenig@....com>
To:     Michael Walle <michael@...le.cc>,
        Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Sumit Semwal <sumit.semwal@...aro.org>
Cc:     linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] i2c: at91: use dma safe buffers

Am 03.03.22 um 17:17 schrieb Michael Walle:
> The supplied buffer might be on the stack and we get the following error
> message:
> [    3.312058] at91_i2c e0070600.i2c: rejecting DMA map of vmalloc memory
>
> Use i2c_{get,put}_dma_safe_msg_buf() to get a DMA-able memory region if
> necessary.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Michael Walle <michael@...le.cc>
> ---
>
> I'm not sure if or which Fixes: tag I should add to this patch. The issue
> seems to be since a very long time, but nobody seem to have triggered it.
> FWIW, I'm using the sff,sfp driver, which triggers this.
>
>   drivers/i2c/busses/i2c-at91-master.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/drivers/i2c/busses/i2c-at91-master.c b/drivers/i2c/busses/i2c-at91-master.c
> index b0eae94909f4..a7a22fedbaba 100644
> --- a/drivers/i2c/busses/i2c-at91-master.c
> +++ b/drivers/i2c/busses/i2c-at91-master.c
> @@ -656,6 +656,7 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
>   	unsigned int_addr_flag = 0;
>   	struct i2c_msg *m_start = msg;
>   	bool is_read;
> +	u8 *dma_buf;

Maybe call your variable differently. DMA-buf is an inter driver buffer 
sharing frame we use for GPU acceleration and V4L.

It doesn't cause any technical issues, but the maintainer regex now 
triggers on that. So you are CCing people not related to this code in 
any way.

Regards,
Christian.

>   
>   	dev_dbg(&adap->dev, "at91_xfer: processing %d messages:\n", num);
>   
> @@ -703,7 +704,18 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
>   	dev->msg = m_start;
>   	dev->recv_len_abort = false;
>   
> +	if (dev->use_dma) {
> +		dma_buf = i2c_get_dma_safe_msg_buf(m_start, 1);
> +		if (!dma_buf) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}
> +		dev->buf = dma_buf;
> +	}
> +
> +
>   	ret = at91_do_twi_transfer(dev);
> +	i2c_put_dma_safe_msg_buf(dma_buf, m_start, !ret);
>   
>   	ret = (ret < 0) ? ret : num;
>   out: