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

Jani Nikula
2015-04-08T08:05:26Z

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