From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:51269) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RzgFw-0001Po-IB for qemu-devel@nongnu.org; Mon, 20 Feb 2012 22:19:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RzgFv-0006qp-Ex for qemu-devel@nongnu.org; Mon, 20 Feb 2012 22:19:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:19200) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RzgFv-0006nq-6r for qemu-devel@nongnu.org; Mon, 20 Feb 2012 22:19:07 -0500 Date: Tue, 21 Feb 2012 05:18:55 +0200 From: "Michael S. Tsirkin" Message-ID: <20120221031854.GA2502@redhat.com> References: <1323870202-25742-1-git-send-email-stefanb@linux.vnet.ibm.com> <1323870202-25742-3-git-send-email-stefanb@linux.vnet.ibm.com> <20120220220201.GD19278@redhat.com> <4F42E899.3010907@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F42E899.3010907@linux.vnet.ibm.com> Subject: Re: [Qemu-devel] [PATCH V14 2/7] Add TPM (frontend) hardware interface (TPM TIS) to Qemu List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Berger Cc: qemu-devel@nongnu.org, andreas.niederl@iaik.tugraz.at On Mon, Feb 20, 2012 at 07:43:05PM -0500, Stefan Berger wrote: > On 02/20/2012 05:02 PM, Michael S. Tsirkin wrote: > >On Wed, Dec 14, 2011 at 08:43:17AM -0500, Stefan Berger wrote: > >>+/* > >>+ * Send a TPM request. > >>+ * Call this with the state_lock held so we can sync with the receive > >>+ * callback. > >>+ */ > >>+static void tpm_tis_tpm_send(TPMState *s, uint8_t locty) > >>+{ > >>+ TPMTISState *tis =&s->s.tis; > >>+ > >>+ tpm_tis_show_buffer(&tis->loc[locty].w_buffer, "tpm_tis: To TPM"); > >>+ > >>+ s->command_locty = locty; > >>+ s->cmd_locty =&tis->loc[locty]; > >>+ > >>+ /* w_offset serves as length indicator for length of data; > >>+ it's reset when the response comes back */ > >>+ tis->loc[locty].status = TPM_TIS_STATUS_EXECUTION; > >>+ tis->loc[locty].sts&= ~TPM_TIS_STS_EXPECT; > >>+ > >>+ s->to_tpm_execute = true; > >>+ qemu_cond_signal(&s->to_tpm_cond); > >>+} > >What happens IIUC is that frondend sets to_tpm_execute > >and signals a condition, and backend clears it > >and waits on a condition. > > > >So how about moving all the signalling > >and locking out to backend, and have frontend > >invoke a callback to signal it? > > > >The whole threading thing then becomes a work-around > >for a backend that does not support select, > >instead of spilling out into frontend? > > > > How do I get the lock calls (qemu_mutex_lock(&s->state_lock)) out of > the frontend? Do you want me to add callbacks to the backend > interface for locking (s->be_driver->ops->state_lock(s)) and one for > unlocking (s->be_driver->ops->state_unlock(tpm_be)) of the state > that really belongs to the front-end (state is 's') and invoke it as > shown in parenthesis and still keep s->state_lock around? Ideally > the locks would end up being 'nop's' if select() was available, but > in the end all backend will need to support that lock. > > [The lock protects the common structure so that the thread in the > backend can deliver the response to a request while the OS for > example polls the hardware interface for its current state.] > > > Stefan Well, this is just an idea, please do not take this as a request or anything like that. Maybe it is a dumb one. Maybe something like what you describe. Alternatively, I imagined that you can pass a copy or pointer of the necessary state to the backend, which queues the command and wakes the worker. In the reverse direction, backend queues a response and when OS polls you dequeue it and update state. Can this work? -- MST