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Wed, 07 Oct 2020 09:42:03 -0700 (PDT) MIME-Version: 1.0 References: <20200930225051.889607-1-david.m.ertman@intel.com> <20201001071403.GC31191@kroah.com> <20201003090855.GD114893@kroah.com> <20201005112547.GA401816@kroah.com> <20201007091443.GA822254@kroah.com> <20201007162251.GB5030@sirena.org.uk> In-Reply-To: <20201007162251.GB5030@sirena.org.uk> From: Dan Williams Date: Wed, 7 Oct 2020 09:41:52 -0700 Message-ID: Subject: Re: [PATCH 0/6] Ancillary bus implementation and SOF multi-client support To: Mark Brown Content-Type: text/plain; charset="UTF-8" Cc: "alsa-devel@alsa-project.org" , "tiwai@suse.de" , "gregkh@linuxfoundation.org" , "Sridharan, Ranjani" , "pierre-louis.bossart@linux.intel.com" , "parav@nvidia.com" , "jgg@nvidia.com" , "Ertman, David M" X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" On Wed, Oct 7, 2020 at 9:23 AM Mark Brown wrote: > > On Wed, Oct 07, 2020 at 09:19:32AM -0700, Dan Williams wrote: > > On Wed, Oct 7, 2020 at 2:14 AM gregkh@linuxfoundation.org > > > > "virtual" here means "not real" :) > > > Which of these aux device use cases is not a real device? One of my > > planned usages for this facility is for the NPEM (Native PCIE > > Enclosure Management) mechanism that can appear on any PCIE > > bridge/endpoint. While it is true that the NPEM register set does not > > get its own PCI-b:d:f address on the host bus, it is still > > discoverable by a standard enumeration scheme. It is real auxiliary > > device functionality that can appear on any PCIE device where the > > kernel can now have one common NPEM driver for all instances in the > > topology. > > Some if not all of the SOF cases are entirely software defined by the > firmware downloaded to the audio DSPs. "Software-defined" in the kernel context to me means software Linux kernel developers have control over, so device-mapper devices, other things that show up under /sys/devices/virtual, or /sys/devices/system/memory/. Firmware changing device functionality is more like just-in-time hardware than software-defined. In other words kernel software is not involved in constructing the device functionality.