linux-kernel - Re: [PATCH] spi: rspi: Only enable interrupts when there's a need to wait

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Message-ID: <20140204111423.GT22609@sirena.org.uk>
Date:	Tue, 4 Feb 2014 11:14:23 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	linux-spi@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
Subject: Re: [PATCH] spi: rspi: Only enable interrupts when there's a need to
 wait

On Tue, Feb 04, 2014 at 11:06:24AM +0100, Geert Uytterhoeven wrote:
> From: Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
> 
> rspi_wait_for_interrupt() unconditionally enables interrupts, even when the
> wait condition is already satisfied. This causes a high interrupt load (2
> interrupts/byte for full-duplex Single SPI transfers, 1 interrupt/byte for
> RSPI with TX Only mode, or QSPI in unidirectional Dual or Quad Transfer
> mode).

Applied but I am wondering if the interrupts are really worth it in the
first place especially at higher clock rates - if you can get completion
within a small number of polls it might be more efficient to just do
that rather than take interrupts.

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