linux-kernel - Re: [PATCH v2] drm/vc4: Fix sleeps during the IRQ handler for DSI transactions.

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Message-ID: <1507966084.12309.129.camel@users.sourceforge.net>
Date:   Sat, 14 Oct 2017 09:28:04 +0200
From:   Paul Menzel <paulepanter@...rs.sourceforge.net>
To:     Eric Anholt <eric@...olt.net>
Cc:     Boris Brezillon <boris.brezillon@...e-electrons.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2] drm/vc4: Fix sleeps during the IRQ handler for DSI
 transactions.

Dear Eric,


Some nit picks where stuff contradicts the coding style.

Am Freitag, den 13.10.2017, 17:12 -0700 schrieb Eric Anholt:
> VC4's DSI1 has a bug where the AXI connection is broken for 32-bit
> writes from the CPU, so we use the DMA engine to DMA 32-bit values
> into registers instead.  That sleeps, so we can't do it from the top
> half.
> 
> As a solution, use an interrupt thread so that all our writes happen
> when sleeping is is allowed.
> 
> v2: Use IRQF_ONESHOT (suggested by Boris)
> 
> Signed-off-by: Eric Anholt <eric@...olt.net>
> ---
> 
> Boris, that cleanup ended up working and it looks great.  Thanks!
> 
>  drivers/gpu/drm/vc4/vc4_dsi.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index 554605af344e..3b74fda5662d 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> @@ -1360,6 +1360,25 @@ static void dsi_handle_error(struct vc4_dsi *dsi,
>  	*ret = IRQ_HANDLED;
>  }
>  
> +/* Initial handler for port 1 where we need the reg_dma workaround.
> + * The register DMA writes sleep, so we can't do it in the top half.
> + * Instead we use IRQF_ONESHOT so that the IRQ gets disabled in the
> + * parent interrupt contrller until our interrupt thread is done.
> + */

There should be a “blank comment line” at the beginning [1].

> The preferred style for long (multi-line) comments is:
> 
> /*
>  * This is the preferred style for multi-line
>  * comments in the Linux kernel source code.
>  * Please use it consistently.
>  *
>  * Description:  A column of asterisks on the left side,
>  * with beginning and ending almost-blank lines.
>  */

> +static irqreturn_t vc4_dsi_irq_defer_to_thread_handler(int irq, void *data)
> +{
> +	struct vc4_dsi *dsi = data;
> +	u32 stat = DSI_PORT_READ(INT_STAT);
> +
> +	if (!stat)
> +		return IRQ_NONE;
> +
> +	return IRQ_WAKE_THREAD;
> +}
> +
> +/* Normal IRQ handler for port 0, or the threaded IRQ handler for port
> + * 1 where we need the reg_dma workaround.
> + */
>  static irqreturn_t vc4_dsi_irq_handler(int irq, void *data)
>  {
>  	struct vc4_dsi *dsi = data;
> @@ -1539,8 +1558,16 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
>  	/* Clear any existing interrupt state. */
>  	DSI_PORT_WRITE(INT_STAT, DSI_PORT_READ(INT_STAT));
>  
> -	ret = devm_request_irq(dev, platform_get_irq(pdev, 0),
> -			       vc4_dsi_irq_handler, 0, "vc4 dsi", dsi);
> +	if (dsi->reg_dma_mem) {
> +		ret = devm_request_threaded_irq(dev, platform_get_irq(pdev, 0),
> +						vc4_dsi_irq_defer_to_thread_handler,
> +						vc4_dsi_irq_handler,
> +						IRQF_ONESHOT,
> +						"vc4 dsi", dsi);
> +	} else {
> +		ret = devm_request_irq(dev, platform_get_irq(pdev, 0),
> +				       vc4_dsi_irq_handler, 0, "vc4 dsi", dsi);
> +	}

The braces should be removed [2].

> Do not unnecessarily use braces where a single statement will do.

>  	if (ret) {
>  		if (ret != -EPROBE_DEFER)
>  			dev_err(dev, "Failed to get interrupt: %d\n", ret);


Thanks,

Paul


[1] https://www.kernel.org/doc/html/v4.13/process/coding-style.html#commenting
[2] https://www.kernel.org/doc/html/v4.13/process/coding-style.html#placing-braces-and-spaces
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