Hi Adrian,
* Adrian Hunter <adrian.hunter@xxxxxxxxx> [2010-11-30 15:23:47 +0200]:
> From 8c0f4490d93b67326ff24f6ce1c7e925b08d96b3 Mon Sep 17 00:00:00 2001
> From: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Date: Mon, 22 Nov 2010 11:32:48 +0200
> Subject: [PATCH 1/2] OMAP: DMA: prevent races while setting M idle mode to nostandby
>
> In a couple of OMAP errata cases, sDMA M idle mode must be
> set temporarily to nostandby. If two DMA users were to do
> that at the same time, a race condition would arise.
> Prevent that by using a spin lock and counting up/down the
> number of times nostandby is set/reset.
>
> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> ---
> arch/arm/plat-omap/dma.c | 59 ++++++++++++++++++++++++++++++++++-----------
> 1 files changed, 44 insertions(+), 15 deletions(-)
>
> diff --git a/arch/arm/plat-omap/dma.c b/arch/arm/plat-omap/dma.c
> index a863f55..6158c99 100644
> --- a/arch/arm/plat-omap/dma.c
> +++ b/arch/arm/plat-omap/dma.c
> @@ -139,6 +139,9 @@ static spinlock_t dma_chan_lock;
> static struct omap_dma_lch *dma_chan;
> static void __iomem *omap_dma_base;
>
> +static u32 midlemode_saved;
> +static int midlemode_save_cnt;
> +
> static const u8 omap1_dma_irq[OMAP1_LOGICAL_DMA_CH_COUNT] = {
> INT_DMA_CH0_6, INT_DMA_CH1_7, INT_DMA_CH2_8, INT_DMA_CH3,
> INT_DMA_CH4, INT_DMA_CH5, INT_1610_DMA_CH6, INT_1610_DMA_CH7,
> @@ -1016,6 +1019,41 @@ void omap_start_dma(int lch)
> }
> EXPORT_SYMBOL(omap_start_dma);
>
> +static void midlemode_nostandby(void)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&dma_chan_lock, flags);
> + if (!midlemode_save_cnt) {
> + u32 l;
> +
> + midlemode_saved = dma_read(OCP_SYSCONFIG);
> + l = midlemode_saved;
> + l &= ~DMA_SYSCONFIG_MIDLEMODE_MASK;
> + l |= DMA_SYSCONFIG_MIDLEMODE(DMA_IDLEMODE_NO_IDLE);
> + dma_write(l, OCP_SYSCONFIG);
> + }
> + midlemode_save_cnt += 1;
> + spin_unlock_irqrestore(&dma_chan_lock, flags);
The latest DMA hwmod patch series is already taken care of this
issue through the API's:
https://patchwork.kernel.org/patch/372231/
-Manjunath
[...]
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