Re: [PATCH v4 06/22] drm: omapdrm: Handle FIFO underflow IRQs internally

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On 14/12/16 02:27, Laurent Pinchart wrote:
> As the FIFO underflow IRQ handler just prints an error message to the
> kernel log, simplify the code by not registering one IRQ handler per
> plane but print the messages directly from the main IRQ handler.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
> ---

> +static void omap_irq_fifo_underflow(struct omap_drm_private *priv,
> +				    u32 irqstatus)
> +{
> +	static DEFINE_RATELIMIT_STATE(_rs, DEFAULT_RATELIMIT_INTERVAL,
> +				      DEFAULT_RATELIMIT_BURST);
> +	static const struct {
> +		const char *name;
> +		u32 mask;
> +	} sources[] = {
> +		{ "gfx", DISPC_IRQ_GFX_FIFO_UNDERFLOW },
> +		{ "vid1", DISPC_IRQ_VID1_FIFO_UNDERFLOW },
> +		{ "vid2", DISPC_IRQ_VID2_FIFO_UNDERFLOW },
> +		{ "vid3", DISPC_IRQ_VID3_FIFO_UNDERFLOW },
> +	};
> +
> +	const u32 mask = DISPC_IRQ_GFX_FIFO_UNDERFLOW
> +		       | DISPC_IRQ_VID1_FIFO_UNDERFLOW
> +		       | DISPC_IRQ_VID2_FIFO_UNDERFLOW
> +		       | DISPC_IRQ_VID3_FIFO_UNDERFLOW;
> +	unsigned int i;
> +
> +	spin_lock(&list_lock);
> +	irqstatus &= priv->irq_mask & mask;
> +	spin_unlock(&list_lock);
> +
> +	if (!irqstatus)
> +		return;

This is called every time we get any DSS interrupt, so I think it would
be good to have a fast-path here without the lock: irqstatus & mask.

Or maybe store the enabled underflow irq bits separately from irq_mask,
as the underflow bits are never changed after the initial setup, and
then there's no need for locking.

 Tomi


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