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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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
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 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
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 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
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 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 Mon, 21 Dec 2009 17:18:01 -0500 William Bourque william.bour...@polymtl.ca 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
