Re: [PATCH] DMA: OMAP: Remove extra looping from omap_request_dma

Scott Ellis
2011-07-01T10:54:15Z

A free channel gets found correctly, that's not the problem.

The patch is to eliminate the extra passes through the loop after
free_ch is assigned.

I dropped some printk's into omap_request_dma()

[ 158.375885] inside omap_request_dma()
[ 158.379577] dev_id = 61 ch = 0 free_ch = -1
[ 158.383789] dev_id = 61 ch = 1 free_ch = -1
[ 158.387969] dev_id = 61 ch = 2 free_ch = -1
[ 158.392181] dev_id = 61 ch = 3 free_ch = -1
[ 158.396392] dev_id = 61 ch = 4 free_ch = -1
[ 158.400573] set free_ch = 4 (could break now)
[ 158.403381] dev_id = 61 ch = 5 free_ch = 4
[ 158.407501] dev_id = 61 ch = 6 free_ch = 4
[ 158.411621] dev_id = 61 ch = 7 free_ch = 4
[ 158.415740] dev_id = 61 ch = 8 free_ch = 4
[ 158.419830] dev_id = 61 ch = 9 free_ch = 4
[ 158.423950] dev_id = 61 ch = 10 free_ch = 4
[ 158.428161] dev_id = 61 ch = 11 free_ch = 4
[ 158.432373] dev_id = 61 ch = 12 free_ch = 4
[ 158.436553] dev_id = 61 ch = 13 free_ch = 4
[ 158.440765] dev_id = 61 ch = 14 free_ch = 4
[ 158.444976] dev_id = 61 ch = 15 free_ch = 4
[ 158.449157] dev_id = 61 ch = 16 free_ch = 4
[ 158.453369] dev_id = 61 ch = 17 free_ch = 4
[ 158.457580] dev_id = 61 ch = 18 free_ch = 4
[ 158.461761] dev_id = 61 ch = 19 free_ch = 4
[ 158.465972] dev_id = 61 ch = 20 free_ch = 4
[ 158.470184] dev_id = 61 ch = 21 free_ch = 4
[ 158.474395] dev_id = 61 ch = 22 free_ch = 4
[ 158.478576] dev_id = 61 ch = 23 free_ch = 4
[ 158.482788] dev_id = 61 ch = 24 free_ch = 4
[ 158.486999] dev_id = 61 ch = 25 free_ch = 4
[ 158.491180] dev_id = 61 ch = 26 free_ch = 4
[ 158.495391] dev_id = 61 ch = 27 free_ch = 4
[ 158.499603] dev_id = 61 ch = 28 free_ch = 4
[ 158.503784] dev_id = 61 ch = 29 free_ch = 4
[ 158.507995] dev_id = 61 ch = 30 free_ch = 4
[ 158.512207] dev_id = 61 ch = 31 free_ch = 4
...
[ 4.097991] inside omap_request_dma()
[ 4.101684] dev_id = 62 ch = 0 free_ch = -1
[ 4.105895] dev_id = 62 ch = 1 free_ch = -1
[ 4.110076] dev_id = 62 ch = 2 free_ch = -1
[ 4.114288] dev_id = 62 ch = 3 free_ch = -1
[ 4.118499] dev_id = 62 ch = 4 free_ch = -1
[ 4.122680] set free_ch = 4 (could break now)
[ 4.125488] dev_id = 62 ch = 5 free_ch = 4
[ 4.129608] dev_id = 62 ch = 6 free_ch = 4
[ 4.133728] dev_id = 62 ch = 7 free_ch = 4
[ 4.137847] dev_id = 62 ch = 8 free_ch = 4
[ 4.141937] dev_id = 62 ch = 9 free_ch = 4
[ 4.146057] dev_id = 62 ch = 10 free_ch = 4
[ 4.150268] dev_id = 62 ch = 11 free_ch = 4
[ 4.154479] dev_id = 62 ch = 12 free_ch = 4
[ 4.158660] dev_id = 62 ch = 13 free_ch = 4
[ 4.162872] dev_id = 62 ch = 14 free_ch = 4
[ 4.167083] dev_id = 62 ch = 15 free_ch = 4
[ 4.171264] dev_id = 62 ch = 16 free_ch = 4
[ 4.175476] dev_id = 62 ch = 17 free_ch = 4
[ 4.179687] dev_id = 62 ch = 18 free_ch = 4
[ 4.183868] dev_id = 62 ch = 19 free_ch = 4
[ 4.188079] dev_id = 62 ch = 20 free_ch = 4
[ 4.192291] dev_id = 62 ch = 21 free_ch = 4
[ 4.196502] dev_id = 62 ch = 22 free_ch = 4
[ 4.200683] dev_id = 62 ch = 23 free_ch = 4
[ 4.204895] dev_id = 62 ch = 24 free_ch = 4
[ 4.209106] dev_id = 62 ch = 25 free_ch = 4
[ 4.213287] dev_id = 62 ch = 26 free_ch = 4
[ 4.217498] dev_id = 62 ch = 27 free_ch = 4
[ 4.221710] dev_id = 62 ch = 28 free_ch = 4
[ 4.225891] dev_id = 62 ch = 29 free_ch = 4
[ 4.230102] dev_id = 62 ch = 30 free_ch = 4
[ 4.234313] dev_id = 62 ch = 31 free_ch = 4
...

I was also wondering, what is special about dev_id == 0? The current
code treats that special and does break immediately?

Scott

On Fri, 2011-07-01 at 00:19 -0700, Tony Lindgren wrote:
> * Scott Ellis <scott@jumpnowtek.com> [110629 20:58]:
> > Break from dma channel search when a free one is found.
>
> Care to describe how the current code is not finding a
> free channel currently?
>
> Tony
>
>
> > Signed-off-by: Scott Ellis <scott@jumpnowtek.com>
> > ---
> > arch/arm/plat-omap/dma.c | 5 ++---
> > 1 files changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm/plat-omap/dma.c b/arch/arm/plat-omap/dma.c
> > index c22217c..3d36fcf 100644
> > --- a/arch/arm/plat-omap/dma.c
> > +++ b/arch/arm/plat-omap/dma.c
> > @@ -678,10 +678,9 @@ int omap_request_dma(int dev_id, const char *dev_name,
> >
> > spin_lock_irqsave(&dma_chan_lock, flags);
> > for (ch = 0; ch < dma_chan_count; ch++) {
> > - if (free_ch == -1 && dma_chan[ch].dev_id == -1) {
> > + if (dma_chan[ch].dev_id == -1) {
> > free_ch = ch;
> > - if (dev_id == 0)
> > - break;
> > + break;
> > }
> > }
> > if (free_ch == -1) {
> >

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