Messages in this thread | | | Date | Wed, 11 Jan 2012 20:35:57 +0800 | From | Richard Zhao <> | Subject | Re: [PATCH 6/6] dma/imx-sdma: check whether event_id0 < 32 when set event_mask |
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On Wed, Jan 11, 2012 at 02:37:08PM +0800, Eric Miao wrote: > On Wed, Jan 11, 2012 at 9:47 AM, Richard Zhao > <richard.zhao@freescale.com> wrote: > > On Wed, Jan 11, 2012 at 08:53:23AM +0800, Richard Zhao wrote: > >> On Tue, Jan 10, 2012 at 11:38:39PM +0800, Shawn Guo wrote: > >> > On Tue, Jan 10, 2012 at 10:29:42PM +0800, Richard Zhao wrote: > >> > > On Tue, Jan 10, 2012 at 10:20:10PM +0800, Shawn Guo wrote: > >> > > > On Tue, Jan 10, 2012 at 03:01:50PM +0800, Richard Zhao wrote: > >> > > > > Signed-off-by: Richard Zhao <richard.zhao@linaro.org> > >> > > > > --- > >> > > > > >> > > > I think it deserves a sensible commit message explaining why the patch > >> > > > is needed. > >> > > If event_id0 < 32, 1 << (sdmac->event_id0 - 32) is not zero. > >> This meant to make you clear about the patch. I'll add it in commit > >> message. > > unsigned int t = 31; > > printf("%d %08x\n", t, 1 << (t-32)); > > > > I test above code on both x86 and arm. They shows different results. > > x86: 31 80000000 > > arm: 31 00000000 > > > > I think we still need this patch. we shoud not let it depends on gcc's > > behavior. > > > > Thanks > > Richard > >> > > > >> > My point is you may explain the exact problem you are seeing without > >> > this patch > >> The kernel don't have event_id < 32 case yet. I found the bug when > >> I review the code. > >> > and how the patch helps here. In general, doing so would > >> > win a warm feeling from reviewers much more easily than leaving the > >> > commit message empty there. > >> I understand your point that comment as much as possible. > >> > > Shawn, > > I think Richard has made the issue quite clear here, the original > code does seem to have some problems even to me, who do not > understand the very details of the SDMA: > > - sdmac->event_mask0 = 1 << sdmac->event_id0; > - sdmac->event_mask1 = 1 << (sdmac->event_id0 - 32); > > 1. if sdmac->event_id0 >= 32, which will cause event_mask0 to be incorrect > 2. if sdmac->event_id < 32, sdmac->event_mask1 will be incorrect > > An alternate way is to use the standard bit operations: > > struct sdma_channel { > > ... > > unsigned long event_mask[2]; > > ... > }; > > set_bit(sdmac->event_id0, event_mask); > > Which avoids branch instructions and add a bit protection for the operation > to be atomic enough (event_mask0/1 won't be inconsistent). It's a good idea.
Thanks Richard -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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