-----Original Message----- From: Takashi Iwai [mailto:tiwai@suse.de] Sent: Saturday, August 15, 2015 10:46 PM
On Sat, 15 Aug 2015 15:49:42 +0200, Lin, Mengdong wrote:
-----Original Message----- From: Takashi Iwai [mailto:tiwai@suse.de] Sent: Saturday, August 15, 2015 3:38 PM
On Fri, 14 Aug 2015 22:34:28 +0200, Mark Brown wrote:
On Mon, Aug 10, 2015 at 10:48:37PM +0800, mengdong.lin@intel.com
wrote:
struct snd_soc_tplg_stream_caps { __le32 size; /* in bytes of this structure */ char name[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
- __le64 formats[SND_SOC_TPLG_MAX_FORMATS]; /* supported
formats SNDRV_PCM_FMTBIT_* */
- __le64 formats; /* supported formats SNDRV_PCM_FORMAT_*
*/
Argh, this is *another* ABI change which you've buried in the middle of a series you're sending right at the end of the release cycle (this was sent after -rc6, we may not even get a -rc7...). Given how close we are to the release and the invasiveness of the changes in this series it's very lucky I even saw it before release, I'm reading this on my flight to Plumbers which means my bandwidth next week will be
limited.
Thanks for checking this. Mengdong, if there is a change in uapi/*, this means touching ABI. So, this change isn't acceptable once when the kernel is released. At least, the backward compatibility *must* be kept no matter which version is.
Thanks for your review, Mark and Takashi. This series including the ABI change, is not for v4.2, but is an RFC to adding
DAI/DAI links support in topology.
I'm sorry that I should have explicitly said this in my comments.
Is there some topic branch which can accept topology patches for next
kernel release?
Can we change topology ABI in v4.3?
In general "yes, but only if it's backward-compatible".
Now only Intel SKL driver is using topology code, so the affect should be
limited.
And I feel using bitwise flag is simpler in both user space and in kernel
coding.
Yes, using FMTBIT_* is better, but this must not justify to break ABI. Either we disable this API/ABI for 4.2, or make the change backward compatible.
Many thanks for your clarification! We'd better keep current ABI unchanged to keep backward compatibility.
In addition, does "disable this API/ABI for 4.2" mean disabling all topology features, or only some structures for v4.2? But alsa-lib already integrated this ABI version.
I'm worried that If we have to add new fields to ABI structures, how to keep the backward compatibility.
Thanks Mengdong
We can increase the topology ABI number when there is ABI change, and
the topology driver always checks this version.
It's a big NO, sorry, this isn't acceptable. Again, the kernel must give the backward compatibility. That is, the kernel must accept the old dialect the user space talks if user space wants. You cannot force user space to communicate in a new ABI out of sudden.
So, yes, ABI version bump is needed if you change ABI. But it means that the kernel accepts all ABIs up to this version, not meaning *only* this ABI version.
Hopefully this clarifies the situation.
thanks,
Takashi