sata_sil24: configure max read request size to 4k

Due to request posting limitations, bandwidth of sil3132 is limited to
around 120MB/s with the minimum pci-e payload size (128bytes) which is
used by most consumer systems.  However, write throughput can be
slightly (~3%) increased by increasing the max read requeset size.
Configure it to 4k which is the maximum supported.  This optimization
is also done by SIMG's windows driver.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>

drivers/ata/sata_sil24.c

@@ -1329,6 +1329,11 @@ static int sil24_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 		}
 	}
 
+	/* Set max read request size to 4096.  This slightly increases
+	 * write throughput for pci-e variants.
+	 */
+	pcie_set_readrq(pdev, 4096);
+
 	sil24_init_controller(host);
 
 	pci_set_master(pdev);