Re: [PATCH v2 2/2] drm: bridge: cdns-mhdp8546: Add support for no-hpd

[Laurent Pinchart]

Hi Jayesh,

Thank you for the patch.

On Wed, Apr 05, 2023 at 07:54:40PM +0530, Jayesh Choudhary wrote:
> From: Rahul T R <r-ravikumar@xxxxxx>
> 
> In J721S2 EVMs DP0 hpd is not connected to correct
> hpd pin on SOC, to handle such cases, Add support for
> "no-hpd" property in the device tree node to disable
> hpd

s/hpd/hpd./

You can also reflow the commit message to 72 columns.

> Also change the log level for dpcd read failuers to
> debug, since framework retries 32 times for each read

s/read/read./

Doesn't this apply to writes as well ?

> Signed-off-by: Rahul T R <r-ravikumar@xxxxxx>
> Signed-off-by: Jayesh Choudhary <j-choudhary@xxxxxx>
> ---
>  .../drm/bridge/cadence/cdns-mhdp8546-core.c   | 37 ++++++++++++++++---
>  .../drm/bridge/cadence/cdns-mhdp8546-core.h   |  1 +
>  2 files changed, 33 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> index f6822dfa3805..e177794b069d 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> @@ -54,6 +54,8 @@
>  #include "cdns-mhdp8546-hdcp.h"
>  #include "cdns-mhdp8546-j721e.h"
>  
> +static int cdns_mhdp_update_link_status(struct cdns_mhdp_device *mhdp);
> +
>  static int cdns_mhdp_mailbox_read(struct cdns_mhdp_device *mhdp)
>  {
>  	int ret, empty;
> @@ -749,7 +751,7 @@ static int cdns_mhdp_fw_activate(const struct firmware *fw,
>  	 * MHDP_HW_STOPPED happens only due to driver removal when
>  	 * bridge should already be detached.
>  	 */
> -	if (mhdp->bridge_attached)
> +	if (mhdp->bridge_attached && !mhdp->no_hpd)
>  		writel(~(u32)CDNS_APB_INT_MASK_SW_EVENT_INT,
>  		       mhdp->regs + CDNS_APB_INT_MASK);
>  
> @@ -845,7 +847,7 @@ static ssize_t cdns_mhdp_transfer(struct drm_dp_aux *aux,
>  		ret = cdns_mhdp_dpcd_read(mhdp, msg->address,
>  					  msg->buffer, msg->size);
>  		if (ret) {
> -			dev_err(mhdp->dev,
> +			dev_dbg(mhdp->dev,
>  				"Failed to read DPCD addr %u\n",
>  				msg->address);
>  
> @@ -1738,6 +1740,19 @@ static int cdns_mhdp_attach(struct drm_bridge *bridge,
>  
>  	spin_unlock(&mhdp->start_lock);
>  
> +	if (mhdp->no_hpd) {
> +		ret = wait_event_timeout(mhdp->fw_load_wq,
> +					 mhdp->hw_state == MHDP_HW_READY,
> +					 msecs_to_jiffies(100));
> +		if (ret == 0) {
> +			dev_err(mhdp->dev, "%s: Timeout waiting for fw loading\n",
> +				__func__);
> +			return -ETIMEDOUT;
> +		}
> +
> +		cdns_mhdp_update_link_status(mhdp);
> +		return 0;
> +	}

Missing blank line.

It's not clear to me while you need to wait for the state to change to
MHDP_HW_READY in the no_hpd case. This should be explained in the commit
message.

>  	/* Enable SW event interrupts */
>  	if (hw_ready)
>  		writel(~(u32)CDNS_APB_INT_MASK_SW_EVENT_INT,
> @@ -2256,7 +2271,16 @@ static int cdns_mhdp_update_link_status(struct cdns_mhdp_device *mhdp)
>  
>  	mutex_lock(&mhdp->link_mutex);
>  
> -	mhdp->plugged = cdns_mhdp_detect_hpd(mhdp, &hpd_pulse);
> +	if (mhdp->no_hpd) {
> +		ret = drm_dp_dpcd_read_link_status(&mhdp->aux, status);
> +		hpd_pulse = false;
> +		if (ret < 0)
> +			mhdp->plugged = false;
> +		else
> +			mhdp->plugged = true;

I think there's an issue with how the driver uses mhdp->plugged. In the
no_hpd case, you try to detect if a display is connected by reading the
link status at attach time, and then never update mhdp->plugged. This
means that if no display is connected at that point, functions like
cdns_mhdp_get_edid() will always fail, even if a display gets plugged
later. As the goal of this series is (as far as I understand) support
systems where the HPD signal could be connected to a SoC GPIO instead of
the bridge, I don't think this is good enough.

> +	} else {
> +		mhdp->plugged = cdns_mhdp_detect_hpd(mhdp, &hpd_pulse);
> +	}
>  
>  	if (!mhdp->plugged) {
>  		cdns_mhdp_link_down(mhdp);
> @@ -2451,6 +2475,8 @@ static int cdns_mhdp_probe(struct platform_device *pdev)
>  	mhdp->aux.dev = dev;
>  	mhdp->aux.transfer = cdns_mhdp_transfer;
>  
> +	mhdp->no_hpd = of_property_read_bool(dev->of_node, "cdns,no-hpd");
> +
>  	mhdp->regs = devm_platform_ioremap_resource(pdev, 0);
>  	if (IS_ERR(mhdp->regs)) {
>  		dev_err(dev, "Failed to get memory resource\n");
> @@ -2526,8 +2552,9 @@ static int cdns_mhdp_probe(struct platform_device *pdev)
>  
>  	mhdp->bridge.of_node = pdev->dev.of_node;
>  	mhdp->bridge.funcs = &cdns_mhdp_bridge_funcs;
> -	mhdp->bridge.ops = DRM_BRIDGE_OP_DETECT | DRM_BRIDGE_OP_EDID |
> -			   DRM_BRIDGE_OP_HPD;
> +	mhdp->bridge.ops = DRM_BRIDGE_OP_DETECT | DRM_BRIDGE_OP_EDID;
> +	if (!mhdp->no_hpd)
> +		mhdp->bridge.ops |= DRM_BRIDGE_OP_HPD;
>  	mhdp->bridge.type = DRM_MODE_CONNECTOR_DisplayPort;
>  	if (mhdp->info)
>  		mhdp->bridge.timings = mhdp->info->timings;
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.h b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.h
> index bedddd510d17..6786ccb51387 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.h
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.h
> @@ -388,6 +388,7 @@ struct cdns_mhdp_device {
>  
>  	bool link_up;
>  	bool plugged;
> +	bool no_hpd;
>  
>  	/*
>  	 * "start_lock" protects the access to bridge_attached and

-- 
Regards,

Laurent Pinchart