[PATCH] staging: imx/drm: request irq only after adding the crtc

Hi,

Matt Sealey writes:

On Tue, Feb 19, 2013 at 8:35 AM, Philipp Zabel [off-list ref] wrote:

quoted

If the bootloader already enabled the display, the interrupt handler
will be called as soon as it is registered. If the CRTC is not already
added at this time, the call to imx_drm_handle_vblank will result in
a NULL pointer dereference.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Doesn't this imply that the bootloader doesn't properly quiesce all
interrupt-causing modules and halt all dma operations?

Sean Bean said it best: One does not simply walk into Mordor!

I am not nacking the patch (since it would not change behavior at all
for those scenarios where quiescence of interrupts and dma was done
properly before the handover) but I am really unsure that this sets a
good precedent.. is this all about getting a "glitch free" splash
screen displayed between bootloader and kernel?

IMO its more about defensive programming. Registering an interrupt
handler only after everything that the handler needs has been
initialized is a Good Thing(TM), no matter whether the interrupt could
possibly occur or not.


Lothar Wa?mann
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