From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 8 May 2019 12:06:48 +0200 From: Cornelia Huck Subject: Re: [PATCH 7/7] s390/cio: Remove vfio-ccw checks of command codes Message-ID: <20190508120648.6c40231d.cohuck@redhat.com> In-Reply-To: <5c2b74a9-e1d9-cd63-1284-6544fa4376d9@linux.ibm.com> References: <20190503134912.39756-1-farman@linux.ibm.com> <20190503134912.39756-8-farman@linux.ibm.com> <8625f759-0a2d-09af-c8b5-5b312d854ba1@linux.ibm.com> <7c897993-d146-bf8e-48ad-11a914a04716@linux.ibm.com> <7ac9fb43-8d7a-9e04-8cba-fa4c63dfc413@linux.ibm.com> <1f2e4272-8570-f93f-9d67-a43dcb00fc55@linux.ibm.com> <5c2b74a9-e1d9-cd63-1284-6544fa4376d9@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org List-Archive: List-Post: To: Pierre Morel Cc: Eric Farman , Farhan Ali , Halil Pasic , linux-s390@vger.kernel.org, kvm@vger.kernel.org List-ID: On Wed, 8 May 2019 11:22:07 +0200 Pierre Morel wrote: > The TEST command is used to retrieve the status of the I/O-device > __path__ and do not go up to the device. > I did not find clearly that it does not start a data transfer but I > really do not think it does. > May be we should ask people from hardware. > I only found that test I/O (a specific test command) do not initiate an > operation. FWIW, I'm not sure about what we should do with the test command in any case. Currently, I see it defined as a proper command in the rather ancient "Common I/O Device Commands" (I don't know of any newer public version), which states that it retrieves the status on the parallel interface _only_ (and generates a command reject on the serial interface). IIRC, the parallel interface has been phased out quite some time ago. The current PoP, in contrast, defines this as an _invalid_ command (generating a channel program check). So, while the test command originally was designed to never initiate a data transfer, we now have an invalid command in its place, and we don't know if something else might change in the future (for transfer mode, a test-like command is already defined in the PoP). So, the safest course would probably be to handle the ->cda portion and send the command down. We'll get a check condition on current hardware, but it should be safe if something changes in the future. Of course, asking some hardware folks is not a bad idea, either :)