Re: [PATCH v5 18/21] drm/tegra: Allocate per-engine channel in core code

Thierry Reding
2021-03-23T12:36:16Z

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On Mon, Jan 11, 2021 at 03:00:16PM +0200, Mikko Perttunen wrote:
> To avoid duplication, allocate the per-engine shared channel in the
> core code instead. Once MLOCKs are implemented on Host1x side, we
> can also update this to avoid allocating a shared channel when
> MLOCKs are enabled.
>
> Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
> ---
> drivers/gpu/drm/tegra/drm.c | 11 +++++++++++
> drivers/gpu/drm/tegra/drm.h | 4 ++++
> 2 files changed, 15 insertions(+)

It'd be helpful if the commit message explained what these per-engine
shared channels are used for.

>
> diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
> index cd81b52a9e06..afd3f143c5e0 100644
> --- a/drivers/gpu/drm/tegra/drm.c
> +++ b/drivers/gpu/drm/tegra/drm.c
> @@ -880,6 +880,14 @@ static const struct drm_driver tegra_drm_driver = {
> int tegra_drm_register_client(struct tegra_drm *tegra,
> struct tegra_drm_client *client)
> {
> + /*
> + * When MLOCKs are implemented, change to allocate a shared channel
> + * only when MLOCKs are disabled.
> + */
> + client->shared_channel = host1x_channel_request(&client->base);
> + if (!client->shared_channel)
> + return -EBUSY;
> +
> mutex_lock(&tegra->clients_lock);
> list_add_tail(&client->list, &tegra->clients);
> client->drm = tegra;
> @@ -896,6 +904,9 @@ int tegra_drm_unregister_client(struct tegra_drm *tegra,
> client->drm = NULL;
> mutex_unlock(&tegra->clients_lock);
>
> + if (client->shared_channel)
> + host1x_channel_put(client->shared_channel);
> +
> return 0;
> }
>
> diff --git a/drivers/gpu/drm/tegra/drm.h b/drivers/gpu/drm/tegra/drm.h
> index f38de08e0c95..0f38f159aa8e 100644
> --- a/drivers/gpu/drm/tegra/drm.h
> +++ b/drivers/gpu/drm/tegra/drm.h
> @@ -87,8 +87,12 @@ struct tegra_drm_client {
> struct list_head list;
> struct tegra_drm *drm;
>
> + /* Set by driver */
> unsigned int version;
> const struct tegra_drm_client_ops *ops;
> +
> + /* Set by TegraDRM core */
> + struct host1x_channel *shared_channel;

Perhaps reorder this so that the core-initialized fields are closer to
the top and the client-initialized fields are closer to the bottom? That
seems like a more natural order.

Thierry

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