Add support for DMA coherent skb heads
Allocate dma heads from DMA coherent memory which is mapped
non-cachable. This requires a proprietary change in the kernel that adds
the dma_coherent field to struct sk_buff.
Using DMA coherent (non-cachable) memory only makes sense when using the
fast forwarding path for the NXP (formerly Freescale) QorIQ LS1024A
(formerly Mindspeed Comcerto 2000) SoC.
See Documentation/networking/ls1024a-fastforwarding.txt in our 4.1
kernel for more information.
It should be noted that the DMA coherent approach is different from the
ZONE_DMA_NCNB approach that was used for the 3.2 kernel. In the 3.2
kernel, they repurposed ZONE_DMA as ZONE_DMA_NCNB. They mapped the
entire zone as non-cachable (but bufferable) and hacked the zone
allocator to not fall back from ZONE_NORMAL to ZONE_DMA (ZONE_DMA_NCNB)
under memory pressure. This allowed them to use kmalloc() and friends
on the non-cachable memory area.
Change-Id: If536c91ed0d393d0bc0969e66556fcf8fbccda65
diff --git a/.local-symbols b/.local-symbols
index a558d06..4837225 100644
--- a/.local-symbols
+++ b/.local-symbols
@@ -184,6 +184,7 @@
ATH10K_USE_NCNB_DESCR=
ATH10K_USE_NCNB_SKB=
ATH10K_USE_COMCERTO_WIFI_FASTPATH=
+ATH10K_USE_DMA_COHERENT_SKB=
WCN36XX=
WCN36XX_DEBUGFS=
B43=
diff --git a/drivers/net/wireless/ath/ath10k/Kconfig b/drivers/net/wireless/ath/ath10k/Kconfig
index bf01fad..47d564a 100644
--- a/drivers/net/wireless/ath/ath10k/Kconfig
+++ b/drivers/net/wireless/ath/ath10k/Kconfig
@@ -52,6 +52,7 @@
config ATH10K_USE_NCNB_DESCR
bool "Atheros support for GFP_DMA_NCNB for descriptors"
depends on ATH10K
+ depends on COMCERTO_ZONE_DMA_NCNB
default n
---help---
This option enables use of GFP_DMA_NCNB for descriptors
@@ -61,11 +62,24 @@
config ATH10K_USE_NCNB_SKB
bool "Atheros support for GFP_DMA_NCNB for sk_buffs"
depends on ATH10K
+ depends on COMCERTO_ZONE_DMA_NCNB
default n
---help---
This option enables use of GFP_DMA_NCNB for sk_buffs on
platforms like the Mindspeed Comcerto C2000.
+config ATH10K_USE_DMA_COHERENT_SKB
+ bool "Atheros support for DMA coherent skb heads"
+ depends on ATH10K
+ depends on COMCERTO_DMA_COHERENT_SKB
+ depends on ATH10K_USE_COMCERTO_WIFI_FASTPATH
+ default n
+ ---help---
+ This option enables use of DMA coherent skb heads (data buffers) on
+ platforms like the NXP (formerly Freescale) QorIQ LS1024A
+ (f.k.a. Mindspeed Comcerto 2000). This requires a custom modification
+ to the kernel that adds the dma_coherent field to struct sk_buff.
+
config ATH10K_USE_COMCERTO_WIFI_FASTPATH
bool "Atheros support for comcerto_wifi_rx_fastpath"
depends on ATH10K
diff --git a/drivers/net/wireless/ath/ath10k/htt_rx.c b/drivers/net/wireless/ath/ath10k/htt_rx.c
index a12e399..179dc38 100644
--- a/drivers/net/wireless/ath/ath10k/htt_rx.c
+++ b/drivers/net/wireless/ath/ath10k/htt_rx.c
@@ -103,6 +103,9 @@
#ifdef CPTCFG_ATH10K_USE_NCNB_SKB
skb = __dev_alloc_skb(HTT_RX_BUF_SIZE + HTT_RX_DESC_ALIGN,
GFP_DMA_NCNB | GFP_ATOMIC);
+#elif defined(CPTCFG_ATH10K_USE_DMA_COHERENT_SKB)
+ skb = alloc_dma_coherent_skb(HTT_RX_BUF_SIZE +
+ HTT_RX_DESC_ALIGN);
#else
skb = dev_alloc_skb(HTT_RX_BUF_SIZE + HTT_RX_DESC_ALIGN);
#endif
diff --git a/drivers/net/wireless/ath/ath10k/pci.c b/drivers/net/wireless/ath/ath10k/pci.c
index 2b9f355..fa4c5a7 100644
--- a/drivers/net/wireless/ath/ath10k/pci.c
+++ b/drivers/net/wireless/ath/ath10k/pci.c
@@ -398,6 +398,8 @@
#ifdef CPTCFG_ATH10K_USE_NCNB_SKB
skb = __dev_alloc_skb(pipe->buf_sz,
GFP_DMA_NCNB | GFP_ATOMIC);
+#elif defined(CPTCFG_ATH10K_USE_DMA_COHERENT_SKB)
+ skb = alloc_dma_coherent_skb(HTT_RX_BUF_SIZE + HTT_RX_DESC_ALIGN);
#else
skb = dev_alloc_skb(pipe->buf_sz);
#endif
diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 6da1ca5..5e726ff 100644
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -2113,6 +2113,41 @@
/* fastpath handled this packet */
slowpath = 0;
}
+#ifdef CPTCFG_ATH10K_USE_DMA_COHERENT_SKB
+ else {
+ if (skb->dma_coherent) {
+ /*
+ * We must never inject DMA coherent skb heads
+ * into the kernel which is why we copy the skb
+ * into normal memory. The reason we must avoid
+ * DMA coherent memory is that struct
+ * skb_shared_info is stored at the end of the
+ * skb head. This struct has a field named
+ * dataref which is defiend as atomic_t, and
+ * ARM prohibits atomic operations on memory
+ * that is not normal. In practice,
+ * __skb_clone() hangs at
+ * atomic_inc(&(skb_shinfo(skb)->dataref));
+ * when it tries to operate on DMA coherent
+ * (non-cachable) memory.
+ *
+ * One of the situations where this code path
+ * is executed is when we receive multicast
+ * frames. comcerto_wifi_rx_fastpath() always
+ * rejects multicast frames which is why we end
+ * up here. The bridge code might have to clone
+ * these frames because they need to be copied
+ * to multiple output ports. Hence, we need to
+ * move the data buffer into normal memory. */
+ struct sk_buff *n = skb_copy(skb, GFP_ATOMIC);
+ consume_skb(skb);
+ if (!n)
+ slowpath = 0;
+ else
+ skb = n;
+ }
+ }
+#endif
if (slowpath)
#endif
{
