Re: [PATCH v9 05/11] drm/fourcc: Add DRM_FORMAT_X403
From: Tomi Valkeinen
Date: Fri Apr 10 2026 - 02:08:20 EST
Hi,
On 26/03/2026 16:43, Simon Ser wrote:
On Wednesday, March 25th, 2026 at 15:02, Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> wrote:
+/*
+ * 3 plane non-subsampled (444) YCbCr
+ * 10 bpc, 30 bits per sample image data in a single contiguous buffer.
+ * index 0: Y plane, [31:0] x:Y2:Y1:Y0 [2:10:10:10] little endian
+ * index 1: Cb plane, [31:0] x:Cb2:Cb1:Cb0 [2:10:10:10] little endian
+ * index 2: Cr plane, [31:0] x:Cr2:Cr1:Cr0 [2:10:10:10] little endian
+ */
+#define DRM_FORMAT_X403 fourcc_code('X', '4', '0', '3')
So, this one is different from the Q family, because Q has padding in
Any idea where the letters (P, Q, S) come from?
LSB rather than MSB. Speaking of, maybe we should add "LSB aligned" to
the doc comment to make that clear?
Yes, I can add that.
Re-reading the sibling thread about DRM_FORMAT_XV20, sounds like the
first digit matches my expectations for sub-sampling. How did you pick
I just used the name in Xilinx's BSP kernel.
the last two digits? I think I would've expected "30" here rather than
"03", since the last two planes are Cb Cr rather than Cr Cb.
Hmm, but X403 is Cb:Cr, and P030 is Cr:Cb, so doesn't 03 make sense here? Oh, but Q401 is Cr:Cb, and it's 01...
Now that I look at this... I think I have to go back and do more testing. From the Xilinx docs, it looks to me that the XV15/XV20 should have the same CrCb order than X403. But the comments in these patches say otherwise. I'm pretty sure my tests conformed to the comments here, but now I don't feel so sure anymore. It's been more than a year since I wrote the tests and properly tested these, so I have to spend a bit time to get everything up again.
Has the first "X" letter been picked arbitrarily? It's already used toI didn't invent the name, I just took the naming Xilinx used. I don't know the history behind it. I assume the "X" is for Xilinx, but I could be wrong here. What would "T" be for? "Tomi"? =)
denote padding in other formats so I wonder if we should pick that
instead of, say, "T".
Tomi