hw/net/imx_fec: return 0xffff when accessing non-existing PHY

If a PHY does not exist, attempts to read from it should return 0xffff.
Otherwise the Linux kernel will believe that a PHY is there and select
the non-existing PHY. This in turn will result in network errors later
on since the real PHY is not selected or configured.

Since reading from or writing to a non-existing PHY is not an emulation
error, replace guest error messages with traces.

Fixes: 461c51ad4275 ("Add a phy-num property to the i.MX FEC emulator")
Cc: Jean-Christophe Dubois <jcd@tribudubois.net>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/imx_fec.c

@@ -283,9 +283,8 @@ static uint32_t imx_phy_read(IMXFECState *s, int reg)
     uint32_t phy = reg / 32;
 
     if (phy != s->phy_num) {
-        qemu_log_mask(LOG_GUEST_ERROR, "[%s.phy]%s: Bad phy num %u\n",
-                      TYPE_IMX_FEC, __func__, phy);
-        return 0;
+        trace_imx_phy_read_num(phy, s->phy_num);
+        return 0xffff;
     }
 
     reg %= 32;
@@ -345,8 +344,7 @@ static void imx_phy_write(IMXFECState *s, int reg, uint32_t val)
     uint32_t phy = reg / 32;
 
     if (phy != s->phy_num) {
-        qemu_log_mask(LOG_GUEST_ERROR, "[%s.phy]%s: Bad phy num %u\n",
-                      TYPE_IMX_FEC, __func__, phy);
+        trace_imx_phy_write_num(phy, s->phy_num);
         return;
     }
 

hw/net/trace-events

@@ -414,7 +414,9 @@ i82596_channel_attention(void *s) "%p: Received CHANNEL ATTENTION"
 
 # imx_fec.c
 imx_phy_read(uint32_t val, int phy, int reg) "0x%04"PRIx32" <= phy[%d].reg[%d]"
+imx_phy_read_num(int phy, int configured) "read request from unconfigured phy %d (configured %d)"
 imx_phy_write(uint32_t val, int phy, int reg) "0x%04"PRIx32" => phy[%d].reg[%d]"
+imx_phy_write_num(int phy, int configured) "write request to unconfigured phy %d (configured %d)"
 imx_phy_update_link(const char *s) "%s"
 imx_phy_reset(void) ""
 imx_fec_read_bd(uint64_t addr, int flags, int len, int data) "tx_bd 0x%"PRIx64" flags 0x%04x len %d data 0x%08x"