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Subject[PATCH v2 2/6] staging: vc04_services: Add comments describing g_cache_line_size.
Date
It's been tempting to replace this with (L1) cache_line_size(), but
that's really not what the value is about. It's about coordinating
the condition for the pagelist fragment behavior between the two
sides.

Signed-off-by: Eric Anholt <eric@anholt.net>
---

v2: new patch to replace the cache_line_size() patch.

.../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 10 +++++++++-
.../staging/vc04_services/interface/vchiq_arm/vchiq_pagelist.h | 1 -
2 files changed, 9 insertions(+), 2 deletions(-)

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 b59ef14890aa..3aeffa189f64 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
@@ -77,7 +77,11 @@ struct vchiq_pagelist_info {
};

static void __iomem *g_regs;
-static unsigned int g_cache_line_size = sizeof(CACHE_LINE_SIZE);
+/* This value is the size of the L2 cache lines as understood by the
+ * VPU firmware, which determines the required alignment of the
+ * offsets/sizes in pagelists.
+ */
+static unsigned int g_cache_line_size = 32;
static unsigned int g_fragments_size;
static char *g_fragments_base;
static char *g_free_fragments;
@@ -117,6 +121,10 @@ int vchiq_platform_init(struct platform_device *pdev, VCHIQ_STATE_T *state)
if (err < 0)
return err;

+ /* Get the L2 cache-line-size as set by the VPU. If the
+ * property is missing, then the firmware assumes an older
+ * kernel using a 32-byte cache line size for compatibility.
+ */
err = of_property_read_u32(dev->of_node, "cache-line-size",
&g_cache_line_size);

diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_pagelist.h b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_pagelist.h
index a6c5f7cc78f0..bec411061554 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_pagelist.h
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_pagelist.h
@@ -34,7 +34,6 @@
#ifndef VCHIQ_PAGELIST_H
#define VCHIQ_PAGELIST_H

-#define CACHE_LINE_SIZE 32
#define PAGELIST_WRITE 0
#define PAGELIST_READ 1
#define PAGELIST_READ_WITH_FRAGMENTS 2
--
2.16.2
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