linux-kernel - Re: [PATCH v2 4/4] media: aspeed: Fix timing polarity incorrect

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Message-ID: <b8707885-c10c-ca19-3f2c-f19f567e1f92@aspeedtech.com>
Date:   Mon, 24 Jan 2022 10:29:46 +0800
From:   Jammy Huang <jammy_huang@...eedtech.com>
To:     Hans Verkuil <hverkuil@...all.nl>, <eajames@...ux.ibm.com>,
        <mchehab@...nel.org>, <joel@....id.au>, <andrew@...id.au>,
        <linux-media@...r.kernel.org>, <openbmc@...ts.ozlabs.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-aspeed@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] media: aspeed: Fix timing polarity incorrect


On 2022/1/21 下午 03:30, Hans Verkuil wrote:
> On 12/22/21 09:21, Jammy Huang wrote:
>> This is a workaround for sync polarity unstable.
>> Sync value get by VR09C counts from sync's rising edge, which means
>> sync's polarity is negative if sync value is bigger than total/2.
> Do you have an example of such a format, or is this mostly theoretical?
>
> Either provide the example or make a note that it is theoretical.

OK, I will update an example in next patch. Let me explain first.

This is a must-be result. Please refer to the graph below as I sent in 
3/4 of this
series. For negative sync, sync width equals to back porch + data enable 
+ front porch.
Thus, sync would be bigger than 90% of total in most cases.

                   +-------------------+
                   |    v i d e o      |
       +--+  +-----+                   +-----+  +---+
          |  |                               |  |
          +--+                               +--+
        vsync+-------------------------------+
    frame_top+-----+
frame_bottom+-------------------------+


Following registers are what I got for 1920x1200@60.

1e700090: 07ee206f 04c9001a c4d3efff 04cc001f

1e7000a0: 0000081f 00000000 00000000 00000000

vertical total = 0x4D3 (VR098[27:16]) = 1235
vertical sync = 0x4CC (VR09C[27:16]) = 1228

>
> Regards,
>
> 	Hans
>
>> Signed-off-by: Jammy Huang <jammy_huang@...eedtech.com>
>> ---
>>   v2:
>>    - Use 'total/2' rather than 'total<<1'
>>    - Update comment
>> ---
>>   drivers/media/platform/aspeed-video.c | 20 ++++++++++++++++++++
>>   1 file changed, 20 insertions(+)
>>
>> diff --git a/drivers/media/platform/aspeed-video.c b/drivers/media/platform/aspeed-video.c
>> index 7c50567f5ab0..c3e3343d91e1 100644
>> --- a/drivers/media/platform/aspeed-video.c
>> +++ b/drivers/media/platform/aspeed-video.c
>> @@ -989,6 +989,16 @@ static void aspeed_video_get_resolution(struct aspeed_video *video)
>>   
>>   		video->frame_bottom = FIELD_GET(VE_SRC_TB_EDGE_DET_BOT, src_tb_edge);
>>   		video->frame_top = FIELD_GET(VE_SRC_TB_EDGE_DET_TOP, src_tb_edge);
>> +
>> +		/*
>> +		 * This is a workaround for polarity detection when the sync
>> +		 * value is larger than half.
>> +		 */
>> +		if (vsync > (vtotal / 2))
>> +			det->polarities &= ~V4L2_DV_VSYNC_POS_POL;
>> +		else
>> +			det->polarities |= V4L2_DV_VSYNC_POS_POL;
>> +
>>   		if (det->polarities & V4L2_DV_VSYNC_POS_POL) {
>>   			det->vbackporch = video->frame_top - vsync;
>>   			det->vfrontporch = vtotal - video->frame_bottom;
>> @@ -1003,6 +1013,16 @@ static void aspeed_video_get_resolution(struct aspeed_video *video)
>>   
>>   		video->frame_right = FIELD_GET(VE_SRC_LR_EDGE_DET_RT, src_lr_edge);
>>   		video->frame_left = FIELD_GET(VE_SRC_LR_EDGE_DET_LEFT, src_lr_edge);
>> +
>> +		/*
>> +		 * This is a workaround for polarity detection when the sync
>> +		 * value is larger than half.
>> +		 */
>> +		if (hsync > (htotal / 2))
>> +			det->polarities &= ~V4L2_DV_HSYNC_POS_POL;
>> +		else
>> +			det->polarities |= V4L2_DV_HSYNC_POS_POL;
>> +
>>   		if (det->polarities & V4L2_DV_HSYNC_POS_POL) {
>>   			det->hbackporch = video->frame_left - hsync;
>>   			det->hfrontporch = htotal - video->frame_right;

-- 
Best Regards
Jammy