net: ethernet: ti: cpsw: extend limits for cpsw_get/set_ringparam

Allow to set number of descs close to possible values. In case of
minimum limit it's equal to number of channels to be able to set
at least one desc per channel. For maximum limit leave enough descs
number for tx channels.
Signed-off-by: NIvan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/cpsw.c

@@ -2493,8 +2493,7 @@ static void cpsw_get_ringparam(struct net_device *ndev,
 	/* not supported */
 	ering->tx_max_pending = 0;
 	ering->tx_pending = cpdma_get_num_tx_descs(cpsw->dma);
-	/* Max 90% RX buffers */
-	ering->rx_max_pending = (descs_pool_size * 9) / 10;
+	ering->rx_max_pending = descs_pool_size - CPSW_MAX_QUEUES;
 	ering->rx_pending = cpdma_get_num_rx_descs(cpsw->dma);
 }
 
@@ -2509,8 +2508,8 @@ static int cpsw_set_ringparam(struct net_device *ndev,
 	/* ignore ering->tx_pending - only rx_pending adjustment is supported */
 
 	if (ering->rx_mini_pending || ering->rx_jumbo_pending ||
-	    ering->rx_pending < (descs_pool_size / 10) ||
-	    ering->rx_pending > ((descs_pool_size * 9) / 10))
+	    ering->rx_pending < CPSW_MAX_QUEUES ||
+	    ering->rx_pending > (descs_pool_size - CPSW_MAX_QUEUES))
 		return -EINVAL;
 
 	if (ering->rx_pending == cpdma_get_num_rx_descs(cpsw->dma))