[U-Boot] [PATCH v3 28/30] net: rtl8169: Properly align buffers

Simon Glass
2014-11-13T01:27:14Z

RX and TX descriptor rings should be aligned to 256 byte boundaries. Use
the DEFINE_ALIGN_BUFFER() macro to define the buffers so that they don't
have to be manually aligned later on. Also make sure that the buffers do
align to cache-line boundaries in case the cache-line is higher than the
256 byte alignment requirements of the NIC.

Also add a warning if the cache-line size is larger than the descriptor
size, because the driver may discard changes to descriptors made by the
hardware when requeuing RX buffers.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
---

Changes in v3: None

drivers/net/rtl8169.c | 63 +++++++++++++++++++++++++++------------------------
1 file changed, 34 insertions(+), 29 deletions(-)

diff --git a/drivers/net/rtl8169.c b/drivers/net/rtl8169.c
index 955b2e1..fc8c31e 100644
--- a/drivers/net/rtl8169.c
+++ b/drivers/net/rtl8169.c
@@ -277,23 +277,41 @@ struct RxDesc {
u32 buf_Haddr;
};

-/* Define the TX Descriptor */
-static u8 tx_ring[NUM_TX_DESC * sizeof(struct TxDesc) + 256];
-/* __attribute__ ((aligned(256))); */
+#define RTL8169_DESC_SIZE 16

-/* Create a static buffer of size RX_BUF_SZ for each
-TX Descriptor. All descriptors point to a
-part of this buffer */
-static unsigned char txb[NUM_TX_DESC * RX_BUF_SIZE];
+#if ARCH_DMA_MINALIGN > 256
+# define RTL8169_ALIGN ARCH_DMA_MINALIGN
+#else
+# define RTL8169_ALIGN 256
+#endif
+
+/*
+ * Warn if the cache-line size is larger than the descriptor size. In such
+ * cases the driver will likely fail because the CPU needs to flush the cache
+ * when requeuing RX buffers, therefore descriptors written by the hardware
+ * may be discarded.
+ */
+#if RTL8169_DESC_SIZE < ARCH_DMA_MINALIGN
+#warning cache-line size is larger than descriptor size
+#endif
+
+/* Define the TX Descriptor */
+DEFINE_ALIGN_BUFFER(struct TxDesc, tx_ring, NUM_TX_DESC, RTL8169_ALIGN);

/* Define the RX Descriptor */
-static u8 rx_ring[NUM_RX_DESC * sizeof(struct TxDesc) + 256];
- /* __attribute__ ((aligned(256))); */
+DEFINE_ALIGN_BUFFER(struct RxDesc, rx_ring, NUM_RX_DESC, RTL8169_ALIGN);

-/* Create a static buffer of size RX_BUF_SZ for each
-RX Descriptor All descriptors point to a
-part of this buffer */
-static unsigned char rxb[NUM_RX_DESC * RX_BUF_SIZE];
+/*
+ * Create a static buffer of size RX_BUF_SZ for each TX Descriptor. All
+ * descriptors point to a part of this buffer.
+ */
+DEFINE_ALIGN_BUFFER(u8, txb, NUM_TX_DESC * RX_BUF_SIZE, RTL8169_ALIGN);
+
+/*
+ * Create a static buffer of size RX_BUF_SZ for each RX Descriptor. All
+ * descriptors point to a part of this buffer.
+ */
+DEFINE_ALIGN_BUFFER(u8, rxb, NUM_RX_DESC * RX_BUF_SIZE, RTL8169_ALIGN);

struct rtl8169_private {
void *mmio_addr; /* memory map physical address */
@@ -301,8 +319,6 @@ struct rtl8169_private {
unsigned long cur_rx; /* Index into the Rx descriptor buffer of next Rx pkt. */
unsigned long cur_tx; /* Index into the Tx descriptor buffer of next Rx pkt. */
unsigned long dirty_tx;
- unsigned char *TxDescArrays; /* Index of Tx Descriptor buffer */
- unsigned char *RxDescArrays; /* Index of Rx Descriptor buffer */
struct TxDesc *TxDescArray; /* Index of 256-alignment Tx Descriptor buffer */
struct RxDesc *RxDescArray; /* Index of 256-alignment Rx Descriptor buffer */
unsigned char *RxBufferRings; /* Index of Rx Buffer */
@@ -711,16 +727,6 @@ static int rtl_reset(struct eth_device *dev, bd_t *bis)
printf ("%s\n", __FUNCTION__);
#endif

- tpc->TxDescArrays = tx_ring;
- /* Tx Desscriptor needs 256 bytes alignment; */
- tpc->TxDescArray = (struct TxDesc *) ((unsigned long)(tpc->TxDescArrays +
- 255) & ~255);
-
- tpc->RxDescArrays = rx_ring;
- /* Rx Desscriptor needs 256 bytes alignment; */
- tpc->RxDescArray = (struct RxDesc *) ((unsigned long)(tpc->RxDescArrays +
- 255) & ~255);
-
rtl8169_init_ring(dev);
rtl8169_hw_start(dev);
/* Construct a perfect filter frame with the mac address as first match
@@ -762,10 +768,6 @@ static void rtl_halt(struct eth_device *dev)

RTL_W32(RxMissed, 0);

- tpc->TxDescArrays = NULL;
- tpc->RxDescArrays = NULL;
- tpc->TxDescArray = NULL;
- tpc->RxDescArray = NULL;
for (i = 0; i < NUM_RX_DESC; i++) {
tpc->RxBufferRing[i] = NULL;
}
@@ -910,6 +912,9 @@ static int rtl_init(struct eth_device *dev, bd_t *bis)
#endif
}

+ tpc->TxDescArray = tx_ring;
+ tpc->RxDescArray = rx_ring;
+
return 1;
}

--
2.1.0.rc2.206.gedb03e5