[PATCH net 10/13] net: stmmac: Make buf_sz module parameter useful

[Serge Semin]

Since the first day of the driver been added to the kernel the Rx
DMA-buffer size module parameter hasn't been utilized for something
more-or-less useful. The STMMAC main code used to initialize the actual Rx
DMA-buffer size (priv->dma_buf_sz) with it by default, but then overwrote
it anyway in accordance with Network device MTU or with default
DMA_BUFFER_SIZE/DEFAULT_BUFSIZE macro. Moreover in the both older and
modern versions of the STMMAC driver the buf_sz module parameter was
overwritten on each Net-dev open procedure with a value calculated in
accordance with MTU and allowed maximum buffer size. Needless to say that
even though it doesn't affect the driver functionality much, setting the
generic parameter with a value specific to a private device is wrong,
seeing each DW MAC may have different maximum buffer size on the same
platform.

In order to finally make the buf_sz (Rx DMA buffer size) parameter really
useful let's stop setting it up with a value specific to a particular
controller and use it to calculate the Rx DMA-buffer size instead of MTU
if one is greater than the later. Thus we'll be able to tune the buffer
size up when it's necessary.

Fixes: 47dd7a540b8a ("net: add support for STMicroelectronics Ethernet controllers.")
Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index e5cb4edc4e23..12de84b7e90d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -100,10 +100,10 @@ static int tc = TC_DEFAULT;
 module_param(tc, int, 0644);
 MODULE_PARM_DESC(tc, "DMA threshold control value");
 
-#define	DEFAULT_BUFSIZE	1536
-static int buf_sz = DEFAULT_BUFSIZE;
-module_param(buf_sz, int, 0644);
-MODULE_PARM_DESC(buf_sz, "DMA buffer size");
+#define DEFAULT_BUFSIZE	1536U
+static unsigned int buf_sz = DEFAULT_BUFSIZE;
+module_param(buf_sz, uint, 0644);
+MODULE_PARM_DESC(buf_sz, "Rx DMA buffer size");
 
 #define	STMMAC_RX_COPYBREAK	256
 
@@ -3730,7 +3730,7 @@ stmmac_setup_dma_desc(struct stmmac_priv *priv, unsigned int mtu)
 		bfsize = 0;
 
 	if (bfsize < BUF_SIZE_16KiB)
-		bfsize = stmmac_set_bfsize(mtu, 0);
+		bfsize = stmmac_set_bfsize(max(buf_sz, mtu), 0);
 
 	dma_conf->dma_buf_sz = bfsize;
 	/* Chose the tx/rx size from the already defined one in the
@@ -3817,7 +3817,6 @@ static int __stmmac_open(struct net_device *dev,
 
 	priv->rx_copybreak = STMMAC_RX_COPYBREAK;
 
-	buf_sz = dma_conf->dma_buf_sz;
 	memcpy(&priv->dma_conf, dma_conf, sizeof(*dma_conf));
 
 	stmmac_reset_queues_param(priv);
-- 
2.39.2