[Intel-gfx] [PATCH] drm/i915: Add debugfs to read any DPCD register

[R, Durgadoss]

>-----Original Message-----
>From: Nikula, Jani
>Sent: Wednesday, April 8, 2015 1:34 PM
>To: R, Durgadoss; intel-gfx at lists.freedesktop.org
>Cc: R, Durgadoss
>Subject: Re: [PATCH] drm/i915: Add debugfs to read any DPCD register
>
>On Wed, 08 Apr 2015, Durgadoss R <durgadoss.r at 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 at 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?

Ok.. Will remove this check in next version..

>
>> +
>> +	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.
 
I added this because we don't have locking constructs for
our state.

For tools, yes, I agree that just a value would do..

Thanks,
Durga

>
>> +	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