netdev - [PATCH net-next 6/6] sfc: simplify DMA mask setting

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Message-ID: <3140001a-66eb-b770-e7b8-c5be71dbd41b@solarflare.com>
Date:   Mon, 7 Sep 2020 17:15:48 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     <linux-net-drivers@...arflare.com>, <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, Christoph Hellwig <hch@...radead.org>
Subject: [PATCH net-next 6/6] sfc: simplify DMA mask setting

Christoph says[1] that dma_set_mask_and_coherent() is smart enough to
 truncate the mask itself if it's too long.  So we can get rid of our
 "lop off one bit and retry" loop in efx_init_io().

[1]: https://www.spinics.net/lists/netdev/msg677266.html

Signed-off-by: Edward Cree <ecree@...arflare.com>
---
 drivers/net/ethernet/sfc/efx_common.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/sfc/efx_common.c b/drivers/net/ethernet/sfc/efx_common.c
index 9eda54e27cd4..80a23def96ad 100644
--- a/drivers/net/ethernet/sfc/efx_common.c
+++ b/drivers/net/ethernet/sfc/efx_common.c
@@ -1086,17 +1086,7 @@ int efx_init_io(struct efx_nic *efx, int bar, dma_addr_t dma_mask,
 
 	pci_set_master(pci_dev);
 
-	/* Set the PCI DMA mask.  Try all possibilities from our
-	 * genuine mask down to 32 bits, because some architectures
-	 * (e.g. x86_64 with iommu_sac_force set) will allow 40 bit
-	 * masks event though they reject 46 bit masks.
-	 */
-	while (dma_mask > 0x7fffffffUL) {
-		rc = dma_set_mask_and_coherent(&pci_dev->dev, dma_mask);
-		if (rc == 0)
-			break;
-		dma_mask >>= 1;
-	}
+	rc = dma_set_mask_and_coherent(&pci_dev->dev, dma_mask);
 	if (rc) {
 		netif_err(efx, probe, efx->net_dev,
 			  "could not find a suitable DMA mask\n");