Em Wed, 20 Jul 2016 23:45:45 +0300 Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> escreveu: > Hi Mauro, > > Mauro Carvalho Chehab wrote: > > Hi Sylwester/Sakari, > > > > While checking the docs for the V4L2 framework, I noticed something weird > > Related to those two flags: > > > > #define V4L2_MBUS_FRAME_DESC_FL_LEN_MAX (1U << 0) > > #define V4L2_MBUS_FRAME_DESC_FL_BLOB (1U << 1) > > > > They were originally introduced by this changeset: > > > > commit 291031192426bfc6ad4ab2eb9fa986025a926598 > > Author: Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx> > > Date: Thu May 17 14:33:30 2012 -0300 > > > > [media] V4L: Add [get/set]_frame_desc subdev callbacks > > > > Add subdev callbacks for setting up parameters of the frame on media bus > > that are not exposed to user space directly. This is just an initial, > > mostly stub implementation. struct v4l2_mbus_frame_desc is intended > > to be extended with sub-structures specific to a particular hardware media > > bus. For now these new callbacks are used only to query or specify maximum > > size of a compressed or hybrid (container) media bus frame in octets. > > > > Signed-off-by: Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx> > > Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> > > Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> > > > > And the comments were modified by this one: > > > > commit 174d6a39b07f51212c23a8e30a0440598d18392c > > Author: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> > > Date: Wed Dec 18 08:40:28 2013 -0300 > > > > [media] v4l: V4L2_MBUS_FRAME_DESC_FL_BLOB is about 1D DMA > > > > V4L2_MBUS_FRAME_DESC_FL_BLOB intends to say the receiver must use 1D DMA to > > receive the image, as the format does not have line offsets. This typically > > includes all compressed formats. > > > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> > > Cc: Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx> > > Signed-off-by: Mauro Carvalho Chehab <m.chehab@xxxxxxxxxxx> > > > > The problem is that the description of V4L2_MBUS_FRAME_DESC_FL_LEN_MAX > > says that: > > Indicates the @length field specifies maximum data length. > > > > But the description of the @length field says otherwise: > > * @length: number of octets per frame, valid if V4L2_MBUS_FRAME_DESC_FL_BLOB > > > > So, I decided to take a look on what the heck is that: > > > > $ git grep V4L2_MBUS_FRAME_DESC_FL_BLOB > > include/media/v4l2-subdev.h:#define V4L2_MBUS_FRAME_DESC_FL_BLOB (1U << 1) > > include/media/v4l2-subdev.h: * %V4L2_MBUS_FRAME_DESC_FL_BLOB. > > include/media/v4l2-subdev.h: * @length: number of octets per frame, valid if V4L2_MBUS_FRAME_DESC_FL_BLOB > > > > (nobody is using it) > > > > And: > > > > $ git grep V4L2_MBUS_FRAME_DESC_FL_LEN_MAX > > drivers/media/i2c/m5mols/m5mols_core.c: fd->entry[0].flags = V4L2_MBUS_FRAME_DESC_FL_LEN_MAX; > > drivers/media/i2c/m5mols/m5mols_core.c: fd->entry[0].flags = V4L2_MBUS_FRAME_DESC_FL_LEN_MAX; > > include/media/v4l2-subdev.h:#define V4L2_MBUS_FRAME_DESC_FL_LEN_MAX (1U << 0) > > > > Only one driver is using it. > > > > So, I'm thinking if are there any reason why to keep the > > V4L2_MBUS_FRAME_DESC_FL_BLOB, and what's the expected behavior > > when V4L2_MBUS_FRAME_DESC_FL_LEN_MAX is found. > > > > Could you shed some light? > > There isn't really a problem that I could see here, except that the > m5mols driver should perhaps set the BLOB flag to indicate it's using > 1-dimensional DMA. Hmm... why both flags should be on? I mean, if they both have the same meaning, we can get rid of one of them. > > What comes to the flags, the LEN_MAX flag indicates that the length > specified in the frame descriptor is the maximum length whereas the real > amount of data could be less than that. Not sure if I understood. Are you saying that, instead of: * @length: number of octets per frame, valid if V4L2_MBUS_FRAME_DESC_FL_BLOB * is set It should be: * @length: number of octets per frame, valid if V4L2_MBUS_FRAME_DESC_FL_LEN_MAX * is set as the description of V4L2_MBUS_FRAME_DESC_FL_LEN_MAX suggests? > The BLOB flag indicates > 1-dimensional DMA, but no driver (yet) uses two-dimensional DMA with > frame descriptors. The patch adding two-dimensional support is here: > > <URL:http://git.retiisi.org.uk/?p=~sailus/linux.git;a=commitdiff;h=b701bd4160410739b165e19327bb64ce25fc509d> > > AFAIR I posted it to linux-media long time ago but the set currently is > still unfinished. It will be needed to add support for sensor embedded > data, for instance. Certain newer sensors also provide more distinct > types of data than the usual (embedded data and image data). Well, if the feature using it was not merged, then we can just wipe it out, re-adding when needed (or eventually changing to something else if the current definition is not ok). Thanks, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
