Public bug reported:

[Impact]
Changing the channel parameters of an hns3 device (ethtool -L) has an 
unintended side-effect of resetting the ring parameters back to their defaults. 
If a user has applied custom ring parameters (ethtool -G), they will be lost.

[Test Case]
Set custom ring parameters:
  $ sudo ethtool -G <hns3-dev> rx 512 tx 512
Verify the change:
  $ sudo ethtool -g <hns3-dev>
  Ring parameters for <hns3-dev>:
  Pre-set maximums:
  RX:           32768
  RX Mini:      0
  RX Jumbo:     0
  TX:           32768
  Current hardware settings:
  RX:           512
  RX Mini:      0
  RX Jumbo:     0
  TX:           512
Now modify the ring parameters:
  sudo ethtool -L <hns3-dev> combined 4
And noticed that the channel parameters are now back at their defaults:
  $ sudo ethtool -g <hns3-dev>
  Ring parameters for <hns3-dev>:
  Pre-set maximums:
  RX:           32768
  RX Mini:      0
  RX Jumbo:     0
  TX:           32768
  Current hardware settings:
  RX:           1024
  RX Mini:      0
  RX Jumbo:     0
  TX:           1024

[Fix]
commit 128b900de7df567ca7ca063bf5da4ed0f357db8c
Author: Yunsheng Lin <linyunsh...@huawei.com>
Date:   Tue Aug 14 17:13:16 2018 +0100

    net: hns3: Fix desc num set to default when setting channel

[Regression Risk]
Localized to a single driver, tested on the one SoC that includes this device.

** Affects: linux (Ubuntu)
     Importance: Undecided
     Assignee: dann frazier (dannf)
         Status: In Progress

** Affects: linux (Ubuntu Bionic)
     Importance: Undecided
     Assignee: dann frazier (dannf)
         Status: In Progress

** Also affects: linux (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu Bionic)
       Status: New => In Progress

** Changed in: linux (Ubuntu Bionic)
     Assignee: (unassigned) => dann frazier (dannf)

** Description changed:

  [Impact]
  Changing the channel parameters of an hns3 device (ethtool -L) has an 
unintended side-effect of resetting the ring parameters back to their defaults. 
If a user has applied custom ring parameters (ethtool -G), they will be lost.
  
  [Test Case]
  Set custom ring parameters:
-   $ sudo ethtool -G <hns3-dev> rx 512 tx 512
+   $ sudo ethtool -G <hns3-dev> rx 512 tx 512
  Verify the change:
-   $ sudo ethtool -g enp125s0f2
-   Ring parameters for enp125s0f2:
-   Pre-set maximums:
-   RX:         32768
-   RX Mini:    0
-   RX Jumbo:   0
-   TX:         32768
-   Current hardware settings:
-   RX:         512
-   RX Mini:    0
-   RX Jumbo:   0
-   TX:         512
+   $ sudo ethtool -g <hns3-dev>
+   Ring parameters for <hns3-dev>:
+   Pre-set maximums:
+   RX:         32768
+   RX Mini:    0
+   RX Jumbo:   0
+   TX:         32768
+   Current hardware settings:
+   RX:         512
+   RX Mini:    0
+   RX Jumbo:   0
+   TX:         512
  Now modify the ring parameters:
-   sudo ethtool -L <hns3-dev> enp124s0f2 combined 4
+   sudo ethtool -L <hns3-dev> combined 4
  And noticed that the channel parameters are now back at their defaults:
-   $ sudo ethtool -g enp125s0f2
-   Ring parameters for enp125s0f2:
-   Pre-set maximums:
-   RX:         32768
-   RX Mini:    0
-   RX Jumbo:   0
-   TX:         32768
-   Current hardware settings:
-   RX:         1024
-   RX Mini:    0
-   RX Jumbo:   0
-   TX:         1024
+   $ sudo ethtool -g <hns3-dev>
+   Ring parameters for <hns3-dev>:
+   Pre-set maximums:
+   RX:         32768
+   RX Mini:    0
+   RX Jumbo:   0
+   TX:         32768
+   Current hardware settings:
+   RX:         1024
+   RX Mini:    0
+   RX Jumbo:   0
+   TX:         1024
  
  [Fix]
  commit 128b900de7df567ca7ca063bf5da4ed0f357db8c
  Author: Yunsheng Lin <linyunsh...@huawei.com>
  Date:   Tue Aug 14 17:13:16 2018 +0100
  
-     net: hns3: Fix desc num set to default when setting channel
+     net: hns3: Fix desc num set to default when setting channel
  
  [Regression Risk]
  Localized to a single driver, tested on the one SoC that includes this device.

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https://bugs.launchpad.net/bugs/1793404

Title:
  hns3: Modifying channel parameters will reset ring parameters back to
  defaults

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