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Date: Sun, 23 Feb 2020 17:32:49 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Ville Syrjälä <ville.syrjala@...ux.intel.com>,
Kees Cook <keescook@...omium.org>
Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@...el.com>,
intel-gfx@...ts.freedesktop.org,
Alexander Potapenko <glider@...gle.com>,
linux-kernel@...r.kernel.org
Subject: Re: [Intel-gfx] [PATCH v2] drm/i915: Distribute switch variables for initialization
On Fri, 21 Feb 2020, Ville Syrjälä <ville.syrjala@...ux.intel.com> wrote:
> On Thu, Feb 20, 2020 at 04:05:17PM -0800, Kees Cook wrote:
>> Variables declared in a switch statement before any case statements
>> cannot be automatically initialized with compiler instrumentation (as
>> they are not part of any execution flow). With GCC's proposed automatic
>> stack variable initialization feature, this triggers a warning (and they
>> don't get initialized). Clang's automatic stack variable initialization
>> (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
>> doesn't initialize such variables[1]. Note that these warnings (or silent
>> skipping) happen before the dead-store elimination optimization phase,
>> so even when the automatic initializations are later elided in favor of
>> direct initializations, the warnings remain.
>>
>> To avoid these problems, move such variables into the "case" where
>> they're used or lift them up into the main function body.
>>
>> drivers/gpu/drm/i915/display/intel_display.c: In function ‘check_digital_port_conflicts’:
>> drivers/gpu/drm/i915/display/intel_display.c:12963:17: warning: statement will never be executed [-Wswitch-unreachable]
>> 12963 | unsigned int port_mask;
>> | ^~~~~~~~~
>>
>> drivers/gpu/drm/i915/intel_pm.c: In function ‘vlv_get_fifo_size’:
>> drivers/gpu/drm/i915/intel_pm.c:474:7: warning: statement will never be executed [-Wswitch-unreachable]
>> 474 | u32 dsparb, dsparb2, dsparb3;
>> | ^~~~~~
>> drivers/gpu/drm/i915/intel_pm.c: In function ‘vlv_atomic_update_fifo’:
>> drivers/gpu/drm/i915/intel_pm.c:1997:7: warning: statement will never be executed [-Wswitch-unreachable]
>> 1997 | u32 dsparb, dsparb2, dsparb3;
>> | ^~~~~~
>>
>> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>> v2: remove port_mask entirely (Ville Syrjälä)
>> v1: https://lore.kernel.org/lkml/20200220062258.68854-1-keescook@chromium.org
>> ---
>> drivers/gpu/drm/i915/display/intel_display.c | 7 ++-----
>> drivers/gpu/drm/i915/intel_pm.c | 4 ++--
>> 2 files changed, 4 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
>> index 064dd99bbc49..5f8c61932e82 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display.c
>> +++ b/drivers/gpu/drm/i915/display/intel_display.c
>> @@ -12960,7 +12960,6 @@ static bool check_digital_port_conflicts(struct intel_atomic_state *state)
>> WARN_ON(!connector_state->crtc);
>>
>> switch (encoder->type) {
>> - unsigned int port_mask;
>> case INTEL_OUTPUT_DDI:
>> if (WARN_ON(!HAS_DDI(to_i915(dev))))
>> break;
>> @@ -12968,13 +12967,11 @@ static bool check_digital_port_conflicts(struct intel_atomic_state *state)
>> case INTEL_OUTPUT_DP:
>> case INTEL_OUTPUT_HDMI:
>> case INTEL_OUTPUT_EDP:
>> - port_mask = 1 << encoder->port;
>> -
>> /* the same port mustn't appear more than once */
>> - if (used_ports & port_mask)
>> + if (used_ports & BIT(encoder->port))
>> ret = false;
>>
>> - used_ports |= port_mask;
>> + used_ports |= BIT(encoder->port);
>
> Thanks. Looks good.
>
> Reviewed-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
Thanks for the patch and review, pushed to dinq.
BR,
Jani.
>
>> break;
>> case INTEL_OUTPUT_DP_MST:
>> used_mst_ports |=
>> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
>> index bd2d30ecc030..17d8833787c4 100644
>> --- a/drivers/gpu/drm/i915/intel_pm.c
>> +++ b/drivers/gpu/drm/i915/intel_pm.c
>> @@ -469,9 +469,9 @@ static void vlv_get_fifo_size(struct intel_crtc_state *crtc_state)
>> struct vlv_fifo_state *fifo_state = &crtc_state->wm.vlv.fifo_state;
>> enum pipe pipe = crtc->pipe;
>> int sprite0_start, sprite1_start;
>> + u32 dsparb, dsparb2, dsparb3;
>>
>> switch (pipe) {
>> - u32 dsparb, dsparb2, dsparb3;
>> case PIPE_A:
>> dsparb = I915_READ(DSPARB);
>> dsparb2 = I915_READ(DSPARB2);
>> @@ -1969,6 +1969,7 @@ static void vlv_atomic_update_fifo(struct intel_atomic_state *state,
>> const struct vlv_fifo_state *fifo_state =
>> &crtc_state->wm.vlv.fifo_state;
>> int sprite0_start, sprite1_start, fifo_size;
>> + u32 dsparb, dsparb2, dsparb3;
>>
>> if (!crtc_state->fifo_changed)
>> return;
>> @@ -1994,7 +1995,6 @@ static void vlv_atomic_update_fifo(struct intel_atomic_state *state,
>> spin_lock(&uncore->lock);
>>
>> switch (crtc->pipe) {
>> - u32 dsparb, dsparb2, dsparb3;
>> case PIPE_A:
>> dsparb = intel_uncore_read_fw(uncore, DSPARB);
>> dsparb2 = intel_uncore_read_fw(uncore, DSPARB2);
>> --
>> 2.20.1
>>
>>
>> --
>> Kees Cook
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx@...ts.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Jani Nikula, Intel Open Source Graphics Center
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