Re: [PATCH] drm/vc4: Fix oops dereferencing DPI's connector since panel_bridge.

From: Boris Brezillon
Date: Wed May 02 2018 - 16:29:40 EST


On Fri, 9 Mar 2018 15:32:56 -0800
Eric Anholt <eric@xxxxxxxxxx> wrote:

> In the cleanup, I didn't notice that we needed to dereference the
> connector for the bus_format. Fix the regression by looking up the
> first (and only) connector attached to us, and assume that its
> bus_format is what we want. Some day it would be good to have that
> part of display_info attached to the bridge, instead.
>
> Signed-off-by: Eric Anholt <eric@xxxxxxxxxx>
> Fixes: 7b1298e05310 ("drm/vc4: Switch DPI to using the panel-bridge helper.")
> Cc: Boris Brezillon <boris.brezillon@xxxxxxxxxxx>

Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxx>

> ---
> drivers/gpu/drm/vc4/vc4_dpi.c | 27 +++++++++++++++++++++++----
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_dpi.c b/drivers/gpu/drm/vc4/vc4_dpi.c
> index 72c9dbd81d7f..88783e143cc2 100644
> --- a/drivers/gpu/drm/vc4/vc4_dpi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dpi.c
> @@ -96,7 +96,6 @@ struct vc4_dpi {
> struct platform_device *pdev;
>
> struct drm_encoder *encoder;
> - struct drm_connector *connector;
>
> void __iomem *regs;
>
> @@ -164,14 +163,31 @@ static void vc4_dpi_encoder_disable(struct drm_encoder *encoder)
>
> static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
> {
> + struct drm_device *dev = encoder->dev;
> struct drm_display_mode *mode = &encoder->crtc->mode;
> struct vc4_dpi_encoder *vc4_encoder = to_vc4_dpi_encoder(encoder);
> struct vc4_dpi *dpi = vc4_encoder->dpi;
> + struct drm_connector_list_iter conn_iter;
> + struct drm_connector *connector = NULL, *connector_scan;
> u32 dpi_c = DPI_ENABLE | DPI_OUTPUT_ENABLE_MODE;
> int ret;
>
> - if (dpi->connector->display_info.num_bus_formats) {
> - u32 bus_format = dpi->connector->display_info.bus_formats[0];
> + /* Look up the connector attached to DPI so we can get the
> + * bus_format. Ideally the bridge would tell us the
> + * bus_format we want, but it doesn't yet, so assume that it's
> + * uniform throughout the bridge chain.
> + */
> + drm_connector_list_iter_begin(dev, &conn_iter);
> + drm_for_each_connector_iter(connector_scan, &conn_iter) {
> + if (connector_scan->encoder == encoder) {
> + connector = connector_scan;
> + break;
> + }
> + }
> + drm_connector_list_iter_end(&conn_iter);
> +
> + if (connector && connector->display_info.num_bus_formats) {
> + u32 bus_format = connector->display_info.bus_formats[0];
>
> switch (bus_format) {
> case MEDIA_BUS_FMT_RGB888_1X24:
> @@ -199,6 +215,9 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
> DRM_ERROR("Unknown media bus format %d\n", bus_format);
> break;
> }
> + } else {
> + /* Default to 24bit if no connector found. */
> + dpi_c |= VC4_SET_FIELD(DPI_FORMAT_24BIT_888_RGB, DPI_FORMAT);
> }
>
> if (mode->flags & DRM_MODE_FLAG_NHSYNC)
> @@ -264,7 +283,7 @@ static int vc4_dpi_init_bridge(struct vc4_dpi *dpi)
> return ret;
> }
>
> - if (panel)
> + if (panel)
> bridge = drm_panel_bridge_add(panel, DRM_MODE_CONNECTOR_DPI);
>
> return drm_bridge_attach(dpi->encoder, bridge, NULL);