linux-kernel - Re: [PATCH 2/2] spi_bitbang: Add support for non-blocking synchronous transfers

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Date:	Sat, 28 Feb 2009 10:09:14 +0100
From:	Simon Kagstrom <simon.kagstrom@...il.com>
To:	Balaji Rao <balajirrao@...nmoko.org>
Cc:	linux-kernel@...r.kernel.org,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Andy Green <andy@...nmoko.com>,
	spi-devel-general@...ts.sourceforge.net
Subject: Re: [PATCH 2/2] spi_bitbang: Add support for non-blocking
 synchronous transfers

Thanks for taking this up Balaji!

In the comment below I'm assuming the Openmoko accelerometer use of
this functionality, which would include doing SPI transfers in the
interrupt handler.

On Sat, 28 Feb 2009 13:41:17 +0530
Balaji Rao <balajirrao@...nmoko.org> wrote:

> +/* Synchronous non blocking transfer */
> +int
> +spi_bitbang_transfer_sync(struct spi_device *spi, struct spi_message
> *m) +{
> [...]
> +		if (setup_transfer) {
> +			status = setup_transfer(spi, t);
> [...]
> +			if (!m->is_dma_mapped)
> +				t->rx_dma = t->tx_dma = 0;
> +			status = bitbang->txrx_bufs(spi, t);

Another thing that we'd need to take care of is that the stuff being
called from the synhronous transfer is actually callable from interrupt
context. Looking at txrx_bufs for s3c24xx (s3c24xx_spi_txrx), it's
using a wait_for_completion which is in turn completed by the s3c24xx
SPI interrupt handler.

Without trying, I'm guessing that that won't be possible from interrupt
context.

// Simon
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