Re: Fatal DMA error problem with netbook and BCM4312 - Test 2
On Mon, 21 Dec 2009 17:18:01 -0500 William Bourque wrote: > Larry Finger wrote: > > Hi, > > > > I placed a number of test prints in my system trying to find where a > > DMA data error might occur. In doing so, I found that 3 slots in the > > DMA header cache cross a page boundary. Such a situation is allowed > > on my system, but it might be forbidden on Atom processors. Please > > try this really ugly hack to see if it makes any difference. > > I confirm that the DMA error is still present with this patch. Ditto. Chris ___ Bcm43xx-dev mailing list Bcm43xx-dev@lists.berlios.de https://lists.berlios.de/mailman/listinfo/bcm43xx-dev
Re: Fatal DMA error problem with netbook and BCM4312 - Test 2
On Monday 21 December 2009 23:20:06 Larry Finger wrote: > Here, it was slot 74 that crossed the page boundary. At 110 bytes per > every 2 slots, that works out to 4070 bytes for 0 - 73. From that, I > infer that the cache starts on a page boundary. Yeah well. For you. -- Greetings, Michael. ___ Bcm43xx-dev mailing list Bcm43xx-dev@lists.berlios.de https://lists.berlios.de/mailman/listinfo/bcm43xx-dev
Re: Fatal DMA error problem with netbook and BCM4312 - Test 2
On 12/21/2009 04:18 PM, William Bourque wrote: > > > Larry Finger wrote: >> Hi, >> >> I placed a number of test prints in my system trying to find where a >> DMA data error might occur. In doing so, I found that 3 slots in the >> DMA header cache cross a page boundary. Such a situation is allowed on >> my system, but it might be forbidden on Atom processors. Please try >> this really ugly hack to see if it makes any difference. > > I confirm that the DMA error is still present with this patch. Thanks for testing. The results are as Michael expected, and as I feared. Larry ___ Bcm43xx-dev mailing list Bcm43xx-dev@lists.berlios.de https://lists.berlios.de/mailman/listinfo/bcm43xx-dev
Re: Fatal DMA error problem with netbook and BCM4312 - Test 2
On 12/21/2009 04:11 PM, Michael Buesch wrote: > On Monday 21 December 2009 23:02:39 Larry Finger wrote: >> On 12/21/2009 03:47 PM, Michael Buesch wrote: >>> On Monday 21 December 2009 22:31:10 Larry Finger wrote: Hi, I placed a number of test prints in my system trying to find where a DMA data error might occur. In doing so, I found that 3 slots in the DMA header cache cross a page boundary. Such a situation is allowed on my system, but it might be forbidden on Atom processors. Please try this really ugly hack to see if it makes any difference. >>> >>> First thing is that the DMA buffers are allowed to cross any boundary (and >>> the header is just a buffer). The boundary requirements only apply to the >>> memory holding the descriptors. >> >> That is what we will test for the Atom. I know it doesn't matter for >> my CPU, but ... > > I'm pretty sure the broadcom DMA engine is not _that_ braindead. > (It is pretty weird, but not _that_ weird). > It would effectively mean that we'd have to bouncebuffer _every_ TX packet. I'm not that worried about the Broadcom implementation as I am about the support chips on the Netbooks. >>> Second thing is: How does the patch prevent a boundary crossing? >> >> The number of slots is reduced to the point that the header cache fits >> in one page, just as the RX header cache does. As I said, this is >> really ugly. If this fixes the problem, then a more elegant fix will >> be needed. > > But the allocation is not required to be aligned to the page start. > The first header might start at offset 4000 of a page, so you cross > the page border after the first few headers. Here, it was slot 74 that crossed the page boundary. At 110 bytes per every 2 slots, that works out to 4070 bytes for 0 - 73. From that, I infer that the cache starts on a page boundary. Larry ___ Bcm43xx-dev mailing list Bcm43xx-dev@lists.berlios.de https://lists.berlios.de/mailman/listinfo/bcm43xx-dev
Re: Fatal DMA error problem with netbook and BCM4312 - Test 2
Larry Finger wrote: > Hi, > > I placed a number of test prints in my system trying to find where a > DMA data error might occur. In doing so, I found that 3 slots in the > DMA header cache cross a page boundary. Such a situation is allowed on > my system, but it might be forbidden on Atom processors. Please try > this really ugly hack to see if it makes any difference. I confirm that the DMA error is still present with this patch. - William > > Thanks, > > Larry > ___ Bcm43xx-dev mailing list Bcm43xx-dev@lists.berlios.de https://lists.berlios.de/mailman/listinfo/bcm43xx-dev
Re: Fatal DMA error problem with netbook and BCM4312 - Test 2
On Monday 21 December 2009 23:02:39 Larry Finger wrote: > On 12/21/2009 03:47 PM, Michael Buesch wrote: > > On Monday 21 December 2009 22:31:10 Larry Finger wrote: > >> Hi, > >> > >> I placed a number of test prints in my system trying to find where a > >> DMA data error might occur. In doing so, I found that 3 slots in the > >> DMA header cache cross a page boundary. Such a situation is allowed on > >> my system, but it might be forbidden on Atom processors. Please try > >> this really ugly hack to see if it makes any difference. > > > > First thing is that the DMA buffers are allowed to cross any boundary (and > > the header is just a buffer). The boundary requirements only apply to the > > memory holding the descriptors. > > That is what we will test for the Atom. I know it doesn't matter for > my CPU, but ... I'm pretty sure the broadcom DMA engine is not _that_ braindead. (It is pretty weird, but not _that_ weird). It would effectively mean that we'd have to bouncebuffer _every_ TX packet. > > Second thing is: How does the patch prevent a boundary crossing? > > The number of slots is reduced to the point that the header cache fits > in one page, just as the RX header cache does. As I said, this is > really ugly. If this fixes the problem, then a more elegant fix will > be needed. But the allocation is not required to be aligned to the page start. The first header might start at offset 4000 of a page, so you cross the page border after the first few headers. -- Greetings, Michael. ___ Bcm43xx-dev mailing list Bcm43xx-dev@lists.berlios.de https://lists.berlios.de/mailman/listinfo/bcm43xx-dev
Re: Fatal DMA error problem with netbook and BCM4312 - Test 2
On 12/21/2009 03:47 PM, Michael Buesch wrote: > On Monday 21 December 2009 22:31:10 Larry Finger wrote: >> Hi, >> >> I placed a number of test prints in my system trying to find where a >> DMA data error might occur. In doing so, I found that 3 slots in the >> DMA header cache cross a page boundary. Such a situation is allowed on >> my system, but it might be forbidden on Atom processors. Please try >> this really ugly hack to see if it makes any difference. > > First thing is that the DMA buffers are allowed to cross any boundary (and > the header is just a buffer). The boundary requirements only apply to the > memory holding the descriptors. That is what we will test for the Atom. I know it doesn't matter for my CPU, but ... > Second thing is: How does the patch prevent a boundary crossing? The number of slots is reduced to the point that the header cache fits in one page, just as the RX header cache does. As I said, this is really ugly. If this fixes the problem, then a more elegant fix will be needed. Larry ___ Bcm43xx-dev mailing list Bcm43xx-dev@lists.berlios.de https://lists.berlios.de/mailman/listinfo/bcm43xx-dev
Re: Fatal DMA error problem with netbook and BCM4312 - Test 2
On Monday 21 December 2009 22:31:10 Larry Finger wrote: > Hi, > > I placed a number of test prints in my system trying to find where a > DMA data error might occur. In doing so, I found that 3 slots in the > DMA header cache cross a page boundary. Such a situation is allowed on > my system, but it might be forbidden on Atom processors. Please try > this really ugly hack to see if it makes any difference. First thing is that the DMA buffers are allowed to cross any boundary (and the header is just a buffer). The boundary requirements only apply to the memory holding the descriptors. Second thing is: How does the patch prevent a boundary crossing? -- Greetings, Michael. ___ Bcm43xx-dev mailing list Bcm43xx-dev@lists.berlios.de https://lists.berlios.de/mailman/listinfo/bcm43xx-dev
Fatal DMA error problem with netbook and BCM4312 - Test 2
Hi,
I placed a number of test prints in my system trying to find where a
DMA data error might occur. In doing so, I found that 3 slots in the
DMA header cache cross a page boundary. Such a situation is allowed on
my system, but it might be forbidden on Atom processors. Please try
this really ugly hack to see if it makes any difference.
Thanks,
Larry
Index: wireless-testing/drivers/net/wireless/b43/dma.h
===
--- wireless-testing.orig/drivers/net/wireless/b43/dma.h
+++ wireless-testing/drivers/net/wireless/b43/dma.h
@@ -160,7 +160,7 @@ struct b43_dmadesc_generic {
#define B43_DMA0_RX_FRAMEOFFSET30
/* DMA engine tuning knobs */
-#define B43_TXRING_SLOTS 256
+#define B43_TXRING_SLOTS 74
#define B43_RXRING_SLOTS 64
#define B43_DMA0_RX_BUFFERSIZE IEEE80211_MAX_FRAME_LEN
___
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