No sound on loudspeaker (Trisquel 12 on macbook 2017)

I installed Trisquel 12 on a retina macbook 2017. Everything works except wifi (that was expected, but it works with a USB wifi adapter) but also, I have no sound on the speakers. If I plug in a headset, there is sound on it.

I see

$ lspci |grep -i audio
00:1f.3 Audio device: Intel Corporation Sunrise Point-LP HD Audio (rev 21)
$ cat /proc/asound/pcm 
00-00: CS4208 Analog : CS4208 Analog : playback 1 : capture 1
00-03: HDMI 0 : HDMI 0 : playback 1
00-07: HDMI 1 : HDMI 1 : playback 1
00-08: HDMI 2 : HDMI 2 : playback 1
$ lspci -v |grep snd
	Kernel driver in use: snd_hda_intel
	Kernel modules: snd_hda_intel, snd_soc_skl, snd_soc_avs, snd_sof_pci_intel_skl

Before I installed Trisquel, this laptop was running MacOS and the sound was working on the speaker, so the speaker is not defective.

Any idea is welcome.