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SubjectRe: [PATCH v1 1/5] drm/tegra: dc: Balance IOMMU group refcounting
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On 04.05.2018 13:45, Thierry Reding wrote:
> 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@gmail.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.

Indeed.

>> + 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.

tegra->group is only used by the dc.c and seems its sole purpose is to avoid
re-attaching DC group if DC0 and DC1 share the same group, like DC's on newer
Tegra's do. I think it's better to rename 'group' to 'dc_group' for the clarity.

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