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

Jani Nikula
2015-04-08T08:52:14Z

On Wed, 08 Apr 2015, "R, Durgadoss" <durgadoss.r@intel.com> wrote:
>>-----Original Message-----
>>From: Nikula, Jani
>>Sent: Wednesday, April 8, 2015 1:34 PM
>>To: R, Durgadoss; intel-gfx@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@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?
>
> Ok.. Will remove this check in next version..

Maybe we should check for some of the intermediate steps in figuring out
intel_dp instead. I know, my dpcd dump doesn't do that either... :(

BR,
Jani.

>
>>
>>> +
>>> + 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

--
Jani Nikula, Intel Open Source Technology Center