linux-kernel - Re: [PATCH 3/3] drm/msm/dp: add a debugfs node for using tpg

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Message-ID: <2193c915-cdda-416d-8e24-209e808c6d10@quicinc.com>
Date: Tue, 3 Dec 2024 19:57:25 -0800
From: Abhinav Kumar <quic_abhinavk@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        "Marijn
 Suijten" <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Stephen Boyd <swboyd@...omium.org>,
        "Kuogee
 Hsieh" <quic_khsieh@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        Jessica Zhang <quic_jesszhan@...cinc.com>
Subject: Re: [PATCH 3/3] drm/msm/dp: add a debugfs node for using tpg



On 12/3/2024 3:38 PM, Dmitry Baryshkov wrote:
> On Mon, Dec 02, 2024 at 12:42:00PM -0800, Abhinav Kumar wrote:
>> DP test pattern generator is a very useful tool to debug issues
>> where monitor is showing incorrect output as it helps to isolate
>> whether the issue is due to rest of DPU pipeline or in the DP
>> controller itself. Expose a debugfs to use the TPG configuration
>> to help debug DP issues.
>>
>> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
>> ---
>>   drivers/gpu/drm/msm/dp/dp_debug.c | 61 +++++++++++++++++++++++++++++++++++++++
>>   drivers/gpu/drm/msm/dp/dp_panel.h |  2 ++
>>   2 files changed, 63 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/msm/dp/dp_debug.c b/drivers/gpu/drm/msm/dp/dp_debug.c
>> index 22fd946ee201..843fe77268f8 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_debug.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_debug.c
>> @@ -197,6 +197,65 @@ static const struct file_operations test_active_fops = {
>>   	.write = msm_dp_test_active_write
>>   };
>>   
>> +static ssize_t msm_dp_tpg_write(struct file *file, const char __user *ubuf,
>> +				size_t len, loff_t *offp)
>> +{
>> +	const struct msm_dp_debug_private *debug;
>> +	char *input_buffer;
>> +	int val;
>> +	int status = 0;
>> +	struct msm_dp_panel *dp_panel;
>> +
>> +	debug = ((struct seq_file *)file->private_data)->private;
>> +	dp_panel = debug->panel;
>> +
>> +	input_buffer = memdup_user_nul(ubuf, len);
>> +	if (IS_ERR(input_buffer))
>> +		return PTR_ERR(input_buffer);
>> +
>> +	status = kstrtoint(input_buffer, 10, &val);
>> +	if (status < 0) {
>> +		kfree(input_buffer);
>> +		return status;
>> +	}
>> +
>> +	msm_dp_panel_tpg_config(dp_panel, val);
>> +
>> +	dp_panel->tpg_enabled = val;
> 
> Does this need any kind of locking? The driver performs some actions,
> then we write the global state. What if the user in parallel writes
> different values to the file?
> 

Sure, I can add a lock to struct msm_dp_debug_private and use it to 
protect the tpg_write and tpg_reads.

>> +
>> +	kfree(input_buffer);
>> +
>> +	*offp += len;
>> +	return len;
>> +}
>> +
>> +static int msm_dp_tpg_show(struct seq_file *f, void *data)
>> +{
>> +	struct msm_dp_debug_private *debug = f->private;
>> +	struct msm_dp_panel *dp_panel = debug->panel;
>> +
>> +	if (dp_panel->tpg_enabled)
>> +		seq_puts(f, "1");
>> +	else
>> +		seq_puts(f, "0");
>> +
>> +	return 0;
>> +}
>> +
>> +static int msm_dp_tpg_open(struct inode *inode, struct file *file)
>> +{
>> +	return single_open(file, msm_dp_tpg_show, inode->i_private);
>> +}
>> +
>> +static const struct file_operations msm_dp_tpg_fops = {
>> +	.owner = THIS_MODULE,
>> +	.open = msm_dp_tpg_open,
>> +	.read = seq_read,
>> +	.llseek = seq_lseek,
>> +	.release = single_release,
>> +	.write = msm_dp_tpg_write
>> +};
>> +
>>   int msm_dp_debug_init(struct device *dev, struct msm_dp_panel *panel,
>>   		  struct msm_dp_link *link,
>>   		  struct drm_connector *connector,
>> @@ -231,6 +290,8 @@ int msm_dp_debug_init(struct device *dev, struct msm_dp_panel *panel,
>>   		debugfs_create_file("dp_test_type", 0444,
>>   				    root,
>>   				    debug, &msm_dp_test_type_fops);
>> +
>> +		debugfs_create_file("dp_tpg", 0444, root, debug, &msm_dp_tpg_fops);
> 
> I'd say, skip the dp_ part of the name, everything in that dir is
> DP-related.
> 

Ack.