On Wed, 2021-03-24 at 17:47 +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> When CONFIG_OF is disabled, building with 'make W=1' produces warnings
> about out of bounds array access:
>
> drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
> drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]
>
> Add an error check before the index is used, which helps with the
> warning, as well as any possible other error condition that may be
> triggered at runtime.
>
> The warning could be fixed by adding a Kconfig depedency on CONFIG_OF,
> but Liu Ying points out that the driver may hit the out-of-bounds
> problem at runtime anyway.
Almost impossible to hit the out-of-bounds problem at runtime, unless
something wrong happens and makes unexpected parameters(node and/or
encoder) be handed over to drm_of_encoder_active_port_id(). Anyway, an
error check on return value from drm_of_encoder_active_port_id() looks
ok to me.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Reviewed-by: Liu Ying <victor.liu@xxxxxxx>
Thanks,
Liu Ying
> ---
> v3: fix build regression from v2
> v2: fix subject line
> expand patch description
> print mux number
> check upper bound as well
> ---
> drivers/gpu/drm/imx/imx-ldb.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
> index dbfe39e2f7f6..565482e2b816 100644
> --- a/drivers/gpu/drm/imx/imx-ldb.c
> +++ b/drivers/gpu/drm/imx/imx-ldb.c
> @@ -197,6 +197,11 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)
> int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
> int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
>
> + if (mux < 0 || mux >= ARRAY_SIZE(ldb->clk_sel)) {
> + dev_warn(ldb->dev, "%s: invalid mux %d\n", __func__, mux);
> + return;
> + }
> +
> drm_panel_prepare(imx_ldb_ch->panel);
>
> if (dual) {
> @@ -255,6 +260,11 @@ imx_ldb_encoder_atomic_mode_set(struct drm_encoder *encoder,
> int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
> u32 bus_format = imx_ldb_ch->bus_format;
>
> + if (mux < 0 || mux >= ARRAY_SIZE(ldb->clk_sel)) {
> + dev_warn(ldb->dev, "%s: invalid mux %d\n", __func__, mux);
> + return;
> + }
> +
> if (mode->clock > 170000) {
> dev_warn(ldb->dev,
> "%s: mode exceeds 170 MHz pixel clock\n", __func__);
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