[PATCH][next] drm/radeon/si_dpm: Replace one-element array with flexible-array in struct SISLANDS_SMC_SWSTATE

[Alex Deucher]

Applied.  Thanks!

Alex

On Wed, Mar 3, 2021 at 2:05 PM Gustavo A. R. Silva
<gustavoars at kernel.org> wrote:
>
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use “flexible array members”[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
>
> Refactor the code according to the use of a flexible-array member in
> struct SISLANDS_SMC_SWSTATE, instead of a one-element array, and use
> the struct_size() helper to calculate the size for the allocation.
>
> Also, this helps with the ongoing efforts to enable -Warray-bounds by
> fixing the following warnings:
>
> drivers/gpu/drm/radeon/si_dpm.c: In function ‘si_convert_power_state_to_smc’:
> drivers/gpu/drm/radeon/si_dpm.c:2350:20: warning: array subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2350 |   smc_state->levels[i].dpm2.MaxPS = (u8)((SISLANDS_DPM2_MAX_PULSE_SKIP * (max_sclk - min_sclk)) / max_sclk);
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/si_dpm.c:2351:20: warning: array subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2351 |   smc_state->levels[i].dpm2.NearTDPDec = SISLANDS_DPM2_NEAR_TDP_DEC;
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/si_dpm.c:2352:20: warning: array subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2352 |   smc_state->levels[i].dpm2.AboveSafeInc = SISLANDS_DPM2_ABOVE_SAFE_INC;
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/si_dpm.c:2353:20: warning: array subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2353 |   smc_state->levels[i].dpm2.BelowSafeInc = SISLANDS_DPM2_BELOW_SAFE_INC;
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/si_dpm.c:2354:20: warning: array subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2354 |   smc_state->levels[i].dpm2.PwrEfficiencyRatio = cpu_to_be16(pwr_efficiency_ratio);
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/si_dpm.c:5105:20: warning: array subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  5105 |   smc_state->levels[i + 1].aT = cpu_to_be32(a_t);
>       |   ~~~~~~~~~~~~~~~~~^~~~~~~
>
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays
>
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/109
> Build-tested-by: kernel test robot <lkp at intel.com>
> Link: https://lore.kernel.org/lkml/603f9a8f.aDLrpMFzzSApzVYQ%25lkp@intel.com/
> Signed-off-by: Gustavo A. R. Silva <gustavoars at kernel.org>
> ---
>  drivers/gpu/drm/radeon/si_dpm.c       |  5 ++---
>  drivers/gpu/drm/radeon/sislands_smc.h | 10 +++++-----
>  2 files changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/si_dpm.c b/drivers/gpu/drm/radeon/si_dpm.c
> index 91bfc4762767..918609551804 100644
> --- a/drivers/gpu/drm/radeon/si_dpm.c
> +++ b/drivers/gpu/drm/radeon/si_dpm.c
> @@ -5250,10 +5250,9 @@ static int si_upload_sw_state(struct radeon_device *rdev,
>         int ret;
>         u32 address = si_pi->state_table_start +
>                 offsetof(SISLANDS_SMC_STATETABLE, driverState);
> -       u32 state_size = sizeof(SISLANDS_SMC_SWSTATE) +
> -               ((new_state->performance_level_count - 1) *
> -                sizeof(SISLANDS_SMC_HW_PERFORMANCE_LEVEL));
>         SISLANDS_SMC_SWSTATE *smc_state = &si_pi->smc_statetable.driverState;
> +       size_t state_size = struct_size(smc_state, levels,
> +                                       new_state->performance_level_count);
>
>         memset(smc_state, 0, state_size);
>
> diff --git a/drivers/gpu/drm/radeon/sislands_smc.h b/drivers/gpu/drm/radeon/sislands_smc.h
> index 966e3a556011..fbd6589bdab9 100644
> --- a/drivers/gpu/drm/radeon/sislands_smc.h
> +++ b/drivers/gpu/drm/radeon/sislands_smc.h
> @@ -182,11 +182,11 @@ typedef struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL SISLANDS_SMC_HW_PERFORMANCE_LEV
>
>  struct SISLANDS_SMC_SWSTATE
>  {
> -    uint8_t                             flags;
> -    uint8_t                             levelCount;
> -    uint8_t                             padding2;
> -    uint8_t                             padding3;
> -    SISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[1];
> +       uint8_t                             flags;
> +       uint8_t                             levelCount;
> +       uint8_t                             padding2;
> +       uint8_t                             padding3;
> +       SISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[];
>  };
>
>  typedef struct SISLANDS_SMC_SWSTATE SISLANDS_SMC_SWSTATE;
> --
> 2.27.0
>
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