Re: [PATCH] drm/i915: Add debugfs to read any DPCD register

[Jani Nikula <jani.nikula@intel.com>]

On Wed, 08 Apr 2015, Durgadoss R <durgadoss.r@intel.com> wrote:
> This patch creates a connector specific debugfs
> interface to read any particular DPCD register.
> The DPCD register address (hex format) is written
> to 'i915_dpcd_addr' interface and the corresponding
> value can be read from 'i915_dpcd_val' interface.
>
> Example usage:
> echo 0x70 > i915_dpcd_addr
> cat i915_dpcd_val
> DPCD[0x70]:0x1

I am still not overjoyed about the interface (because it has a state),
but I don't have anything better to suggest either. I'll defer to others
to make the taste judgement...

Review comments for the implementation inline.

BR,
Jani.


>
> Signed-off-by: Durgadoss R <durgadoss.r@intel.com>
> ---
> This patch is based on top of Jani's patch:
> "add i915 specific connector debugfs file for DPCD"
> [https://freedesktop.org/patch/43332/]

Already committed.

>
>  drivers/gpu/drm/i915/i915_debugfs.c | 102 +++++++++++++++++++++++++++++++++++-
>  drivers/gpu/drm/i915/intel_drv.h    |   1 +
>  2 files changed, 102 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 10ca511..9951d84 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -4865,6 +4865,101 @@ static const struct file_operations i915_dpcd_fops = {
>  	.release = single_release,
>  };
>  
> +static ssize_t i915_dpcd_addr_write(struct file *file, const char __user *ubuf,
> +				     size_t len, loff_t *offp)
> +{
> +	struct seq_file *m = file->private_data;
> +	struct drm_connector *connector = m->private;
> +	struct intel_dp *intel_dp =
> +		enc_to_intel_dp(&intel_attached_encoder(connector)->base);
> +	unsigned int reg_addr;
> +	char tmp[16];
> +	int ret;
> +
> +	if (!intel_dp)
> +		return -EINVAL;

I think it's highly unlikely this will be NULL. You're more likely to
oops above if something went wrong (see enc_to_intel_dp and
intel_attached_encoder). Also, -ENODEV?

> +
> +	if (len >= sizeof(tmp))
> +		return -EINVAL;
> +
> +	if (copy_from_user(tmp, ubuf, len))
> +		return -EFAULT;
> +
> +	tmp[len] = '\0';
> +
> +	ret = sscanf(tmp, "%x\n", &reg_addr);

See kstrtouint.

> +	if (ret == 0)
> +		return -EINVAL;
> +
> +	intel_dp->debugfs_dpcd_addr = reg_addr;
> +
> +	return len;
> +}
> +
> +static int i915_dpcd_addr_show(struct seq_file *m, void *data)
> +{
> +	struct drm_connector *connector = m->private;
> +	struct intel_dp *intel_dp =
> +		enc_to_intel_dp(&intel_attached_encoder(connector)->base);
> +
> +	if (!intel_dp)
> +		return -EINVAL;

Same as above.

> +
> +	seq_printf(m, "0x%x\n", intel_dp->debugfs_dpcd_addr);
> +
> +	return 0;
> +}
> +
> +static int i915_dpcd_addr_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, i915_dpcd_addr_show, inode->i_private);
> +}
> +
> +static const struct file_operations i915_dpcd_addr_fops = {
> +	.owner = THIS_MODULE,
> +	.open = i915_dpcd_addr_open,
> +	.read = seq_read,
> +	.write = i915_dpcd_addr_write,
> +	.llseek = seq_lseek,
> +	.release = single_release,
> +};
> +
> +static int i915_dpcd_val_show(struct seq_file *m, void *data)
> +{
> +	struct drm_connector *connector = m->private;
> +	struct intel_dp *intel_dp =
> +		enc_to_intel_dp(&intel_attached_encoder(connector)->base);
> +	unsigned int addr;
> +	u8 buf[1];

Might be more obvious to just have u8 val, and use a pointer to
it. *shrug*.

> +	int ret;
> +
> +	if (!intel_dp)
> +		return -EINVAL;

Same as above.

> +
> +	addr = intel_dp->debugfs_dpcd_addr;
> +	ret = drm_dp_dpcd_readb(&intel_dp->aux, addr, buf);
> +	if (ret < 0) {
> +		DRM_ERROR("dpcd read for 0x%x failed:%d\n", addr, ret);

I think there'll already be errors in the log at this point. This is
probably redundant.

> +		return ret;
> +	}
> +
> +	seq_printf(m, "DPCD[0x%x]:0x%x\n", addr, buf[0]);

For an interface better suited for tools than humans, I'd drop all the
fluff and just print the content. Maybe use 0x%02x for format.

> +	return 0;
> +}
> +
> +static int i915_dpcd_val_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, i915_dpcd_val_show, inode->i_private);
> +}
> +
> +static const struct file_operations i915_dpcd_val_fops = {
> +	.owner = THIS_MODULE,
> +	.open = i915_dpcd_val_open,
> +	.read = seq_read,
> +	.llseek = seq_lseek,
> +	.release = single_release,
> +};
> +
>  /**
>   * i915_debugfs_connector_add - add i915 specific connector debugfs files
>   * @connector: pointer to a registered drm_connector
> @@ -4883,9 +4978,14 @@ int i915_debugfs_connector_add(struct drm_connector *connector)
>  		return -ENODEV;
>  
>  	if (connector->connector_type == DRM_MODE_CONNECTOR_DisplayPort ||
> -	    connector->connector_type == DRM_MODE_CONNECTOR_eDP)
> +	    connector->connector_type == DRM_MODE_CONNECTOR_eDP) {
>  		debugfs_create_file("i915_dpcd", S_IRUGO, root, connector,
>  				    &i915_dpcd_fops);
> +		debugfs_create_file("i915_dpcd_addr", S_IRUGO | S_IWUSR,
> +				root, connector, &i915_dpcd_addr_fops);
> +		debugfs_create_file("i915_dpcd_val", S_IRUGO, root,
> +				connector, &i915_dpcd_val_fops);
> +	}
>  
>  	return 0;
>  }
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 4799b11..0594baa 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -642,6 +642,7 @@ struct intel_dp {
>  	unsigned long last_power_cycle;
>  	unsigned long last_power_on;
>  	unsigned long last_backlight_off;
> +	unsigned int debugfs_dpcd_addr;
>  
>  	struct notifier_block edp_notifier;
>  
> -- 
> 1.9.1
>

-- 
Jani Nikula, Intel Open Source Technology Center
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