linux-kernel - Re: [PATCH v1 1/5] drm/tegra: dc: Balance IOMMU group refcounting

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Message-ID: <20180504104515.GM13459@ulmo>
Date:   Fri, 4 May 2018 12:45:15 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/5] drm/tegra: dc: Balance IOMMU group refcounting

On Fri, May 04, 2018 at 02:47:19AM +0300, Dmitry Osipenko wrote:
> Remove unneeded iommu_group_get() and add missing iommu_group_put(),
> correcting IOMMU group refcount. This is a minor correction / cleanup that
> doesn't really fix anything because Tegra's IOMMU driver are built-in and
> hence groups refcounting can't hold IOMMU driver from unloading.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/gpu/drm/tegra/dc.c  | 35 +++++++++++++++++------------------
>  drivers/gpu/drm/tegra/dc.h  |  2 +-
>  drivers/gpu/drm/tegra/drm.h |  2 +-
>  3 files changed, 19 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> index d7a0f62c6e2e..9fc34c6a7218 100644
> --- a/drivers/gpu/drm/tegra/dc.c
> +++ b/drivers/gpu/drm/tegra/dc.c
> @@ -1927,7 +1927,6 @@ static irqreturn_t tegra_dc_irq(int irq, void *data)
>  static int tegra_dc_init(struct host1x_client *client)
>  {
>  	struct drm_device *drm = dev_get_drvdata(client->parent);
> -	struct iommu_group *group = iommu_group_get(client->dev);
>  	unsigned long flags = HOST1X_SYNCPT_CLIENT_MANAGED;
>  	struct tegra_dc *dc = host1x_client_to_dc(client);
>  	struct tegra_drm *tegra = drm->dev_private;
> @@ -1939,20 +1938,21 @@ static int tegra_dc_init(struct host1x_client *client)
>  	if (!dc->syncpt)
>  		dev_warn(dc->dev, "failed to allocate syncpoint\n");
>  
> -	if (group && tegra->domain) {
> -		if (group != tegra->group) {
> -			err = iommu_attach_group(tegra->domain, group);
> +	if (tegra->domain) {
> +		dc->group = iommu_group_get(client->dev);
> +
> +		if (dc->group && dc->group != tegra->dc_group) {
> +			err = iommu_attach_group(tegra->domain, dc->group);
>  			if (err < 0) {
>  				dev_err(dc->dev,
>  					"failed to attach to domain: %d\n",
>  					err);
> +				iommu_group_put(dc->group);
>  				return err;
>  			}
>  
> -			tegra->group = group;
> +			tegra->dc_group = dc->group;
>  		}
> -
> -		dc->domain = tegra->domain;
>  	}
>  
>  	if (dc->soc->wgrps)
> @@ -2017,13 +2017,13 @@ static int tegra_dc_init(struct host1x_client *client)
>  	if (!IS_ERR(primary))
>  		drm_plane_cleanup(primary);
>  
> -	if (group && dc->domain) {
> -		if (group == tegra->group) {
> -			iommu_detach_group(dc->domain, group);
> -			tegra->group = NULL;
> +	if (dc->group) {
> +		if (dc->group && dc->group == tegra->dc_group) {

You can drop the dc->group check from the second conditional.

> +			iommu_detach_group(tegra->domain, dc->group);
> +			tegra->dc_group = NULL;
>  		}
>  
> -		dc->domain = NULL;
> +		iommu_group_put(dc->group);
>  	}
>  
>  	return err;
> @@ -2032,7 +2032,6 @@ static int tegra_dc_init(struct host1x_client *client)
>  static int tegra_dc_exit(struct host1x_client *client)
>  {
>  	struct drm_device *drm = dev_get_drvdata(client->parent);
> -	struct iommu_group *group = iommu_group_get(client->dev);
>  	struct tegra_dc *dc = host1x_client_to_dc(client);
>  	struct tegra_drm *tegra = drm->dev_private;
>  	int err;
> @@ -2045,13 +2044,13 @@ static int tegra_dc_exit(struct host1x_client *client)
>  		return err;
>  	}
>  
> -	if (group && dc->domain) {
> -		if (group == tegra->group) {
> -			iommu_detach_group(dc->domain, group);
> -			tegra->group = NULL;
> +	if (dc->group) {
> +		if (dc->group && dc->group == tegra->dc_group) {
> +			iommu_detach_group(tegra->domain, dc->group);
> +			tegra->dc_group = NULL;
>  		}
>  
> -		dc->domain = NULL;
> +		iommu_group_put(dc->group);
>  	}
>  
>  	host1x_syncpt_free(dc->syncpt);
> diff --git a/drivers/gpu/drm/tegra/dc.h b/drivers/gpu/drm/tegra/dc.h
> index ca5cac6bf8ea..5ca4e07333bb 100644
> --- a/drivers/gpu/drm/tegra/dc.h
> +++ b/drivers/gpu/drm/tegra/dc.h
> @@ -94,7 +94,7 @@ struct tegra_dc {
>  
>  	const struct tegra_dc_soc_info *soc;
>  
> -	struct iommu_domain *domain;
> +	struct iommu_group *group;
>  };
>  
>  static inline struct tegra_dc *
> diff --git a/drivers/gpu/drm/tegra/drm.h b/drivers/gpu/drm/tegra/drm.h
> index 4f41aaec8530..7777640a6911 100644
> --- a/drivers/gpu/drm/tegra/drm.h
> +++ b/drivers/gpu/drm/tegra/drm.h
> @@ -46,7 +46,7 @@ struct tegra_drm {
>  	struct drm_device *drm;
>  
>  	struct iommu_domain *domain;
> -	struct iommu_group *group;
> +	struct iommu_group *dc_group;

It's not obvious to me why this needs to be renamed.

Thierry

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