I have noticed that on my Dell E6520 notebook the e-sata hotplugging stopped
working since kernel 4.15.

Currently I can observe this problem with kernel:
4.15.7-1.6-x86_64
4.16.0-rc4-4.g7a5941a-x86-64

The e-sata cable is OK, and an e-sata device can be used with kernel 4.15 if it
is turned on and plugged in before powering on my notebook.

(The e-sata hotplugging works well with the Leap kernel
4.12.14-lp150.5.3-x86_64.)

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(I���m not an advanced user, but I���m ready to follow detailed instructions.)