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    Subject[PATCH 3/3] [RFC] Revert "drm/i915: use variadic macros and arrays to choose port/pipe based registers"
    Date
    The varargs macro trick in _PIPE3/_PHY3/_PORT3 was meant as an optimization
    to shrink the i915 kernel module by around 1000 bytes. However, the
    downside is a size regression with CONFIG_KASAN, as I found from stack size
    warnings with gcc-7.0.1:

    before:
    drivers/gpu/drm/i915/intel_dpll_mgr.c: In function 'bxt_ddi_pll_get_hw_state':
    drivers/gpu/drm/i915/intel_dpll_mgr.c:1644:1: error: the frame size of 176 bytes is larger than 100 bytes [-Werror=frame-larger-than=]
    drivers/gpu/drm/i915/intel_dpll_mgr.c: In function 'bxt_ddi_pll_enable':
    drivers/gpu/drm/i915/intel_dpll_mgr.c:1548:1: error: the frame size of 224 bytes is larger than 100 bytes [-Werror=frame-larger-than=]

    after:
    drivers/gpu/drm/i915/intel_dpll_mgr.c: In function 'bxt_ddi_pll_get_hw_state':
    drivers/gpu/drm/i915/intel_dpll_mgr.c:1644:1: error: the frame size of 1016 bytes is larger than 1000 bytes [-Werror=frame-larger-than=]
    drivers/gpu/drm/i915/intel_dpll_mgr.c: In function 'bxt_ddi_pll_enable':
    drivers/gpu/drm/i915/intel_dpll_mgr.c:1548:1: error: the frame size of 1960 bytes is larger than 1000 bytes [-Werror=frame-larger-than=]

    I also checked the module sizes and got

    before:
    text data bss dec hex filename
    2704592 412025 11104 3127721 2fb9a9 drivers/gpu/drm/i915/i915.o

    after:
    text data bss dec hex filename
    2718538 412025 11104 3141667 2ff023 drivers/gpu/drm/i915/i915.o

    showing a significant code size growth. This reverts the patch to avoid
    the warning and get back to the better code with CONFIG_KASAN. If someone
    has another idea to avoid the warning while keeping the more efficient
    code for the non-KASAN case, that would obviously be better.

    Fixes: ce64645d86ac ("drm/i915: use variadic macros and arrays to choose port/pipe based registers")
    Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    ---
    drivers/gpu/drm/i915/i915_reg.h | 11 ++++++-----
    1 file changed, 6 insertions(+), 5 deletions(-)

    diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
    index 04c8f69fcc62..aa732eccdeb5 100644
    --- a/drivers/gpu/drm/i915/i915_reg.h
    +++ b/drivers/gpu/drm/i915/i915_reg.h
    @@ -48,8 +48,6 @@ static inline bool i915_mmio_reg_valid(i915_reg_t reg)
    return !i915_mmio_reg_equal(reg, INVALID_MMIO_REG);
    }

    -#define _PICK(__index, ...) (((const u32 []){ __VA_ARGS__ })[__index])
    -
    #define _PIPE(pipe, a, b) ((a) + (pipe)*((b)-(a)))
    #define _MMIO_PIPE(pipe, a, b) _MMIO(_PIPE(pipe, a, b))
    #define _PLANE(plane, a, b) _PIPE(plane, a, b)
    @@ -58,11 +56,14 @@ static inline bool i915_mmio_reg_valid(i915_reg_t reg)
    #define _MMIO_TRANS(tran, a, b) _MMIO(_TRANS(tran, a, b))
    #define _PORT(port, a, b) ((a) + (port)*((b)-(a)))
    #define _MMIO_PORT(port, a, b) _MMIO(_PORT(port, a, b))
    -#define _PIPE3(pipe, ...) _PICK(pipe, __VA_ARGS__)
    +#define _PIPE3(pipe, a, b, c) ((pipe) == PIPE_A ? (a) : \
    + (pipe) == PIPE_B ? (b) : (c))
    #define _MMIO_PIPE3(pipe, a, b, c) _MMIO(_PIPE3(pipe, a, b, c))
    -#define _PORT3(port, ...) _PICK(port, __VA_ARGS__)
    +#define _PORT3(port, a, b, c) ((port) == PORT_A ? (a) : \
    + (port) == PORT_B ? (b) : (c))
    #define _MMIO_PORT3(pipe, a, b, c) _MMIO(_PORT3(pipe, a, b, c))
    -#define _PHY3(phy, ...) _PICK(phy, __VA_ARGS__)
    +#define _PHY3(phy, a, b, c) ((phy) == DPIO_PHY0 ? (a) : \
    + (phy) == DPIO_PHY1 ? (b) : (c))
    #define _MMIO_PHY3(phy, a, b, c) _MMIO(_PHY3(phy, a, b, c))

    #define _MASKED_FIELD(mask, value) ({ \
    --
    2.9.0
    \
     
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