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SubjectRe: [PATCH] drm/bridge: Fix Exynos DSI after making bridge chain a double-linked list
On Fri, 27 Dec 2019 14:23:13 +0100
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> On Fri, 27 Dec 2019 13:00:04 +0100
> Boris Brezillon <boris.brezillon@collabora.com> wrote:
>
> > On Fri, 27 Dec 2019 12:01:35 +0100
> > Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> >
> > > Exynos DSI DRM driver uses private calls to out bridge to force certain
> > > order of operations during init/exit sequences. This no longer works after
> > > conversion of bridge chain to a double-linked list. To fix the regression
> > > call bridge related operations manually instead of the generic
> > > drm_bridge_chain_*() operations.
> >
> > I think it'd be worth explaining what the problem is (infinite loop
> > caused by list_for_each_entry() use when the bridge is no longer part
> > of the chain attached to the encoder).
> >
> > >
> > > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> > > Fixes: 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked list")
> >
> > We also need to fix that in VC4.
> >
> > > ---
> > > This patch is a result of the following discussion:
> > > https://www.spinics.net/lists/dri-devel/msg239256.html
> > > ---
> > > drivers/gpu/drm/exynos/exynos_drm_dsi.c | 21 ++++++++++++---------
> > > 1 file changed, 12 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> > > index 3955f84dc893..f5905c239a86 100644
> > > --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> > > +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> > > @@ -255,7 +255,6 @@ struct exynos_dsi {
> > > struct mipi_dsi_host dsi_host;
> > > struct drm_connector connector;
> > > struct drm_panel *panel;
> > > - struct list_head bridge_chain;
> > > struct drm_bridge *out_bridge;
> > > struct device *dev;
> > >
> > > @@ -1391,7 +1390,8 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
> > > if (ret < 0)
> > > goto err_put_sync;
> > > } else {
> > > - drm_bridge_chain_pre_enable(dsi->out_bridge);
> > > + if (dsi->out_bridge->funcs->pre_enable)
> > > + dsi->out_bridge->funcs->pre_enable(dsi->out_bridge);
> >
> > Okay, so you're calling ->{pre_enable,enable,disable,post_disable}() on
> > the first bridge element which only works if the chain contains one
> > bridge (see below). Maybe you should keep exynos_dsi.bridge_chain and
> > create custom helpers to iterate over chain elements instead of calling
> > those hooks only on out_bridge.
>
> The following diff should fix the problem while keeping the solution
> generic enough to support chains containing more than one bridge.
>
> --->8---
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> index 3955f84dc893..c861b640fc59 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> @@ -1378,6 +1378,7 @@ static void exynos_dsi_unregister_te_irq(struct exynos_dsi *dsi)
> static void exynos_dsi_enable(struct drm_encoder *encoder)
> {
> struct exynos_dsi *dsi = encoder_to_dsi(encoder);
> + struct drm_bridge *iter;
> int ret;
>
> if (dsi->state & DSIM_STATE_ENABLED)
> @@ -1391,7 +1392,11 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
> if (ret < 0)
> goto err_put_sync;
> } else {
> - drm_bridge_chain_pre_enable(dsi->out_bridge);
> + list_for_each_entry_reverse(iter, &encoder->bridge_chain,

^&dsi->bridge_chain

And the same applies to all list_for_each() calls in this patch.

> + chain_node) {
> + if (iter->funcs->pre_enable)
> + iter->funcs->pre_enable(iter);
> + }
> }
>
> exynos_dsi_set_display_mode(dsi);
> @@ -1402,7 +1407,10 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
> if (ret < 0)
> goto err_display_disable;
> } else {
> - drm_bridge_chain_enable(dsi->out_bridge);
> + list_for_each_entry(iter, &encoder->bridge_chain, chain_node) {
> + if (iter->funcs->enable)
> + iter->funcs->enable(iter);
> + }
> }
>
> dsi->state |= DSIM_STATE_VIDOUT_AVAILABLE;
> @@ -1420,6 +1428,7 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
> static void exynos_dsi_disable(struct drm_encoder *encoder)
> {
> struct exynos_dsi *dsi = encoder_to_dsi(encoder);
> + struct drm_bridge *iter;
>
> if (!(dsi->state & DSIM_STATE_ENABLED))
> return;
> @@ -1427,10 +1436,20 @@ static void exynos_dsi_disable(struct drm_encoder *encoder)
> dsi->state &= ~DSIM_STATE_VIDOUT_AVAILABLE;
>
> drm_panel_disable(dsi->panel);
> - drm_bridge_chain_disable(dsi->out_bridge);
> +
> + list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
> + if (iter->funcs->disable)
> + iter->funcs->disable(iter);
> + }
> +
> exynos_dsi_set_display_enable(dsi, false);
> drm_panel_unprepare(dsi->panel);
> - drm_bridge_chain_post_disable(dsi->out_bridge);
> +
> + list_for_each_entry(iter, &encoder->bridge_chain, chain_node) {
> + if (iter->funcs->post_disable)
> + iter->funcs->post_disable(iter);
> + }
> +
> dsi->state &= ~DSIM_STATE_ENABLED;
> pm_runtime_put_sync(dsi->dev);
> }
> @@ -1523,7 +1542,7 @@ static int exynos_dsi_host_attach(struct mipi_dsi_host *host,
> if (out_bridge) {
> drm_bridge_attach(encoder, out_bridge, NULL);
> dsi->out_bridge = out_bridge;
> - list_splice(&encoder->bridge_chain, &dsi->bridge_chain);
> + list_splice_init(&encoder->bridge_chain, &dsi->bridge_chain);
> } else {
> int ret = exynos_dsi_create_connector(encoder);
>

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