Re: [PATCH v6 03/11] iommu/mediatek: Add device_link between the consumer and the larb devices

On Wed, 2021-07-14 at 10:26 +0200, Dafna Hirschfeld wrote:

On 14.07.21 04:56, Yong Wu wrote:

quoted

MediaTek IOMMU-SMI diagram is like below. all the consumer connect with
smi-larb, then connect with smi-common.

         M4U
          |
     smi-common
          |
   -------------
   |         |    ...
   |         |
larb1     larb2
   |         |
vdec       venc

When the consumer works, it should enable the smi-larb's power which
also need enable the smi-common's power firstly.

Thus, First of all, use the device link connect the consumer and the
smi-larbs. then add device link between the smi-larb and smi-common.

This patch adds device_link between the consumer and the larbs.

When device_link_add, I add the flag DL_FLAG_STATELESS to avoid calling
pm_runtime_xx to keep the original status of clocks. It can avoid two
issues:
1) Display HW show fastlogo abnormally reported in [1]. At the beggining,
all the clocks are enabled before entering kernel, but the clocks for
display HW(always in larb0) will be gated after clk_enable and clk_disable
called from device_link_add(->pm_runtime_resume) and rpm_idle. The clock
operation happened before display driver probe. At that time, the display
HW will be abnormal.

2) A deadlock issue reported in [2]. Use DL_FLAG_STATELESS to skip
pm_runtime_xx to avoid the deadlock.

Corresponding, DL_FLAG_AUTOREMOVE_CONSUMER can't be added, then
device_link_removed should be added explicitly.

[1] https://lore.kernel.org/linux-mediatek/1564213888.22908.4.camel@mhfsdcap03/ (local)
[2] https://lore.kernel.org/patchwork/patch/1086569/

Suggested-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
---
  drivers/iommu/mtk_iommu.c    | 22 ++++++++++++++++++++++
  drivers/iommu/mtk_iommu_v1.c | 20 +++++++++++++++++++-
  2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
index a02dde094788..ee742900cf4b 100644
--- a/drivers/iommu/mtk_iommu.c
+++ b/drivers/iommu/mtk_iommu.c

@@ -571,22 +571,44 @@ static struct iommu_device *mtk_iommu_probe_device(struct device *dev)
  {
  	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
  	struct mtk_iommu_data *data;
+	struct device_link *link;
+	struct device *larbdev;
+	unsigned int larbid;
  
  	if (!fwspec || fwspec->ops != &mtk_iommu_ops)
  		return ERR_PTR(-ENODEV); /* Not a iommu client device */
  
  	data = dev_iommu_priv_get(dev);
  
+	/*
+	 * Link the consumer device with the smi-larb device(supplier)
+	 * The device in each a larb is a independent HW. thus only link
+	 * one larb here.
+	 */
+	larbid = MTK_M4U_TO_LARB(fwspec->ids[0]);
+	larbdev = data->larb_imu[larbid].dev;
+	link = device_link_add(dev, larbdev,
+			       DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS);
+	if (!link)
+		dev_err(dev, "Unable to link %s\n", dev_name(larbdev));

shoudn't ERR_PTR be returned in case of failure?

In the previous design, this is not a fatal error. the consumer device
could probe continuously even though it fail here..Returning here may
let the issue be caught earlier, I will add this in next version.

 if (!link) {
      ...
      return ERR_PTR(EINVAL);
  }

Thanks,
Dafna

quoted

  	return &data->iommu;
  }
  
  static void mtk_iommu_release_device(struct device *dev)
  {
  	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
+	struct mtk_iommu_data *data;
+	struct device *larbdev;
+	unsigned int larbid;
  
  	if (!fwspec || fwspec->ops != &mtk_iommu_ops)
  		return;
  
+	data = dev_iommu_priv_get(dev);
+	larbid = MTK_M4U_TO_LARB(fwspec->ids[0]);
+	larbdev = data->larb_imu[larbid].dev;
+	device_link_remove(dev, larbdev);
+
  	iommu_fwspec_free(dev);
  }
  

diff --git a/drivers/iommu/mtk_iommu_v1.c b/drivers/iommu/mtk_iommu_v1.c
index d9365a3d8dc9..d2a7c66b8239 100644
--- a/drivers/iommu/mtk_iommu_v1.c
+++ b/drivers/iommu/mtk_iommu_v1.c

@@ -424,7 +424,9 @@ static struct iommu_device *mtk_iommu_probe_device(struct device *dev)
  	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
  	struct of_phandle_args iommu_spec;
  	struct mtk_iommu_data *data;
-	int err, idx = 0;
+	int err, idx = 0, larbid;
+	struct device_link *link;
+	struct device *larbdev;
  
  	while (!of_parse_phandle_with_args(dev->of_node, "iommus",
  					   "#iommu-cells",

@@ -445,6 +447,14 @@ static struct iommu_device *mtk_iommu_probe_device(struct device *dev)
  
  	data = dev_iommu_priv_get(dev);
  
+	/* Link the consumer device with the smi-larb device(supplier) */
+	larbid = mt2701_m4u_to_larb(fwspec->ids[0]);
+	larbdev = data->larb_imu[larbid].dev;
+	link = device_link_add(dev, larbdev,
+			       DL_FLAG_PM_RUNTIME | DL_FLAG_STATELESS);
+	if (!link)
+		dev_err(dev, "Unable to link %s\n", dev_name(larbdev));
+
  	return &data->iommu;
  }
  

@@ -465,10 +475,18 @@ static void mtk_iommu_probe_finalize(struct device *dev)
  static void mtk_iommu_release_device(struct device *dev)
  {
  	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
+	struct mtk_iommu_data *data;
+	struct device *larbdev;
+	unsigned int larbid;
  
  	if (!fwspec || fwspec->ops != &mtk_iommu_ops)
  		return;
  
+	data = dev_iommu_priv_get(dev);
+	larbid = mt2701_m4u_to_larb(fwspec->ids[0]);
+	larbdev = data->larb_imu[larbid].dev;
+	device_link_remove(dev, larbdev);
+
  	iommu_fwspec_free(dev);
  }
  

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