idpf: cap maximum Rx buffer size

The HW only supports a maximum Rx buffer size of 16K-128. On systems
using large pages, the libeth logic can configure the buffer size to be
larger than this. The upper bound is PAGE_SIZE while the lower bound is
MTU rounded up to the nearest power of 2. For example, ARM systems with
a 64K page size and an mtu of 9000 will set the Rx buffer size to 16K,
which will cause the config Rx queues message to fail.

Initialize the bufq/fill queue buf_len field to the maximum supported
size. This will trigger the libeth logic to cap the maximum Rx buffer
size by reducing the upper bound.

Fixes: 74d1412ac8f37 ("idpf: use libeth Rx buffer management for payload buffer")
Signed-off-by: Joshua Hay <[e-mail]>
Acked-by: Alexander Lobakin <[e-mail]>
Reviewed-by: Madhu Chittim <[e-mail]>
Reviewed-by: Jacob Keller <[e-mail]>
Reviewed-by: Aleksandr Loktionov <[e-mail]>
Reviewed-by: David Decotigny <[e-mail]>
Signed-off-by: Tony Nguyen <[e-mail]>

drivers/net/ethernet/intel/idpf/idpf_txrx.c

···
 static int idpf_rx_bufs_init_singleq(struct idpf_rx_queue *rxq)
 {
 	struct libeth_fq fq = {
-		.count	= rxq->desc_count,
-		.type	= LIBETH_FQE_MTU,
-		.nid	= idpf_q_vector_to_mem(rxq->q_vector),
+		.count		= rxq->desc_count,
+		.type		= LIBETH_FQE_MTU,
+		.buf_len	= IDPF_RX_MAX_BUF_SZ,
+		.nid		= idpf_q_vector_to_mem(rxq->q_vector),
 	};
 	int ret;
 
···
 		.truesize	= bufq->truesize,
 		.count		= bufq->desc_count,
 		.type		= type,
+		.buf_len	= IDPF_RX_MAX_BUF_SZ,
 		.hsplit		= idpf_queue_has(HSPLIT_EN, bufq),
 		.xdp		= idpf_xdp_enabled(bufq->q_vector->vport),
 		.nid		= idpf_q_vector_to_mem(bufq->q_vector),

drivers/net/ethernet/intel/idpf/idpf_txrx.h

···
 		idx = 0;					\
 } while (0)
 
+#define IDPF_RX_MAX_BUF_SZ			(16384 - 128)
 #define IDPF_RX_BUF_STRIDE			32
 #define IDPF_RX_BUF_POST_STRIDE			16
 #define IDPF_LOW_WATERMARK			64