linux-kernel - [PATCH] staging: vc04_services: setup DMA and coherent mask

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Message-Id: <20161028171159.23973-1-mzoran@crowfest.net>
Date:   Fri, 28 Oct 2016 10:11:59 -0700
From:   Michael Zoran <mzoran@...wfest.net>
To:     gregkh@...uxfoundation.org
Cc:     eric@...olt.net, swarren@...dotorg.org, lee@...nel.org,
        mzoran@...wfest.net, daniels@...labora.com, noralf@...nnes.org,
        popcornmix@...il.com, linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] staging: vc04_services: setup DMA and coherent mask

Setting the DMA mask is optional on 32 bit but
is mandatory on 64 bit.  Set the DMA mask and coherent
to force all DMA to be in the 32 bit address space.

This is considered a "good practice" and most drivers
already do this.

Signed-off-by: Michael Zoran <mzoran@...wfest.net>
---
 .../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
index a5afcc5..6fa2b5a 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
@@ -97,6 +97,16 @@ int vchiq_platform_init(struct platform_device *pdev, VCHIQ_STATE_T *state)
 	int slot_mem_size, frag_mem_size;
 	int err, irq, i;
 
+	/*
+	 * Setting the DMA mask is necessary in the 64 bit environment.
+	 * It isn't necessary in a 32 bit environment but is considered
+	 * a good practice.
+	 */
+	err = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
+
+	if (err < 0)
+		return err;
+
 	(void)of_property_read_u32(dev->of_node, "cache-line-size",
 				   &g_cache_line_size);
 	g_fragments_size = 2 * g_cache_line_size;
-- 
2.10.1