Hi Laurent, On Wed, Sep 06, 2023 at 04:47:37PM +0300, Laurent Pinchart wrote: > On Wed, Sep 06, 2023 at 01:39:59PM +0000, Sakari Ailus wrote: > > Hi Laurent, > > > > On Wed, Sep 06, 2023 at 04:30:57PM +0300, Laurent Pinchart wrote: > > > On Wed, Sep 06, 2023 at 01:25:53PM +0000, Sakari Ailus wrote: > > > > On Wed, Sep 06, 2023 at 03:36:58PM +0300, Laurent Pinchart wrote: > > > > > On Wed, Sep 06, 2023 at 11:36:45AM +0000, Sakari Ailus wrote: > > > > > > On Tue, Sep 05, 2023 at 07:47:20PM +0300, Laurent Pinchart wrote: > > > > > > > On Fri, Aug 11, 2023 at 09:11:39AM +0000, Sakari Ailus wrote: > > > > > > > > On Fri, Aug 11, 2023 at 08:31:16AM +0200, Jacopo Mondi wrote: > > > > > > > > > > > +V4L2_META_FMT_GENERIC_CSI2_10 > > > > > > > > > > > +----------------------------- > > > > > > > > > > > + > > > > > > > > > > > +V4L2_META_FMT_GENERIC_CSI2_10 contains packed 8-bit generic metadata, 10 bits > > > > > > > > > > > +for each 8 bits of data. Every four bytes of metadata is followed by a single > > > > > > > > > > > +byte of padding. The way the data is stored follows the CSI-2 specification. > > > > > > > > > > > + > > > > > > > > > > > +This format is also used on CSI-2 on 20 bits per sample format that packs two > > > > > > > > > > > +bytes of metadata into one sample. > > > > > > > > > > > + > > > > > > > > > > > +This format is little endian. > > > > > > > > > > > + > > > > > > > > > > > +**Byte Order Of V4L2_META_FMT_GENERIC_CSI2_10.** > > > > > > > > > > > +Each cell is one byte. "M" denotes a byte of metadata and "p" a byte of padding. > > > > > > > > > > > > > > > > > > > > I think you should document whether the padding is always 0 or can be any value. > > > > > > > > > > Perhaps 'X' is a better 'name' for the padding byte in the latter case. > > > > > > > > > > > > > > > > > > Did I get this right that this format is supposed to work as the RAW10 > > > > > > > > > CSI-2 packed image format, where 4 bytes contain the higher 8 bits of > > > > > > > > > the 10 bits sample and the 5th byte every 4 contains the lower 2 bits of > > > > > > > > > the previous 4 sample ? > > > > > > > > > > > > > > > > > > If that's the case, is 'padding' the correct term here ? > > > > > > > > > > > > > > > > What else would you call it? It'll be zeros that exist just due to the bit > > > > > > > > depth used and as such not interesting at all. > > > > > > > > > > > > > > It's actually not 0, CCS requires the padding bytes to be 0x55. > > > > > > > > > > > > > > I wonder if the conformance test suite tests the contents of the padding > > > > > > > bytes. > > > > > > > > > > > > I don't know. I could add the value is unspecified but as it has not been > > > > > > specified, there's no change in meaning (just size). > > > > > > > > > > I started writing that I don't see how it could help applications to > > > > > know that the padding byte is 0x55, but the SMIA++ embedded data parser > > > > > in libcamera actually checks for it, and considers the embedded data to > > > > > be erroneous if it has a different value. > > > > > > > > I think it's fine to check for it if you know it's CCS/SMIA++/SMIA embedded > > > > data. But documenting it here isn't a great idea as then other uses of this > > > > format definition would be excluded. > > > > > > I'm OK with that, but note that you've mentioned in a different patch in > > > the same series that you wouldn't use the CCS media bus code for sensors > > > that are compliant with the CCS packing and encoding but not the CCS > > > register set. That's not very consistent :-) > > > > Which specific patch are you referring to? > > "[PATCH v3 09/10] media: Add media bus codes for MIPI CCS embedded data" > > You wrote > > "There are sensors that aren't fully compatible with CCS (including > those compatible with SMIA and SMIA++) but I wouldn't expect the format > to be used by devices that are entirely incompatible with CCS." Ah, right. I meant that if a sensor implementation isn't related to any of these standards, it's highly unlikely to use the same embedded data format. Of course, if it does, then I think we should use the mbus code, too. But I'm not holding my breath. -- Regards, Sakari Ailus
