Re: [PATCH 5/7] net: stmmac: Program RX queue size and flow control
From: Stephen Warren
Date: Thu Mar 09 2017 - 15:27:31 EST
On 03/09/2017 12:42 PM, Thierry Reding wrote:
On Mon, Feb 27, 2017 at 12:09:02PM +0200, Mikko Perttunen wrote:
On 23.02.2017 19:24, Thierry Reding wrote:
From: Thierry Reding <treding@xxxxxxxxxx>
Program the receive queue size based on the RX FIFO size and enable
hardware flow control for large FIFOs.
diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
@@ -252,6 +253,44 @@ static void dwmac4_dma_chan_op_mode(void __iomem *ioaddr, int txmode,
mtl_rx_op |= MTL_OP_MODE_RTC_128;
}
+ mtl_rx_op &= ~MTL_OP_MODE_RQS_MASK;
+ mtl_rx_op |= rqs << MTL_OP_MODE_RQS_SHIFT;
+
+ /* enable flow control only if each channel gets 4 KiB or more FIFO */
+ if (rxfifosz >= 4096) {
+ unsigned int rfd, rfa;
+
+ mtl_rx_op |= MTL_OP_MODE_EHFC;
+
+ switch (rxfifosz) {
+ case 4096:
+ rfd = 0x03;
+ rfa = 0x01;
+ break;
+
+ case 8192:
+ rfd = 0x06;
+ rfa = 0x0a;
+ break;
+
+ case 16384:
+ rfd = 0x06;
+ rfa = 0x12;
+ break;
+
+ default:
+ rfd = 0x06;
+ rfa = 0x1e;
+ break;
+ }
Are these values correct? In the 4096 case, rfd > rfa, in all other cases
the other way around. In any case it would be useful to have a comment
clarifying the thresholds in bytes.
I'll investigate. To be honest I simply took this from Stephen's U-Boot
driver since that's already tested. I trust Stephen, so I didn't bother
double-checking.
I don't recall for sure, but I think these values came directly from
either the upstream kernel (the non-stmmac driver) or NV downstream
kernel EQoS driver, and I re-used them without investigating. I'm not
even sure if the outer if() expression is true; these numbers might not
even end up being used?