Re: [PATCH 08/14] net: ks8851: Use 16-bit read of RXFC register

On 3/24/20 2:50 AM, Andrew Lunn wrote:

quoted

@@ -470,7 +455,7 @@ static void ks8851_rx_pkts(struct ks8851_net *ks)
 	unsigned rxstat;
 	u8 *rxpkt;
 
-	rxfc = ks8851_rdreg8(ks, KS_RXFC);
+	rxfc = (ks8851_rdreg16(ks, KS_RXFCTR) >> 8) & 0xff;

The datasheet says:

2. When software driver reads back Receive Frame Count (RXFCTR)
Register; the KSZ8851 will update both Receive Frame Header Status and
Byte Count Registers (RXFHSR/RXFHBCR)

Are you sure there is no side affect here?

Yes, look at the RXFC register 0x9c itself. It's a 16bit register, 0x9c
is the LSByte and 0x9d is the MSByte.

What happened here before was readout of register 0x9d, MSByte of RXFC,
which triggers the update of RXFHSR/RXFHBCR. What happens now is the
readout of the whole RXFC as 16bit value, which also triggers the update.