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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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