From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10BD2C433FE for ; Wed, 5 Oct 2022 12:11:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229450AbiJEMLY (ORCPT ); Wed, 5 Oct 2022 08:11:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60036 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229950AbiJEMLV (ORCPT ); Wed, 5 Oct 2022 08:11:21 -0400 Received: from mta-01.yadro.com (mta-02.yadro.com [89.207.88.252]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE4CC2BE3B for ; Wed, 5 Oct 2022 05:11:17 -0700 (PDT) Received: from localhost (unknown [127.0.0.1]) by mta-01.yadro.com (Postfix) with ESMTP id 496ED400F8; Wed, 5 Oct 2022 12:11:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=yadro.com; h= content-transfer-encoding:content-type:content-type:in-reply-to :references:from:from:content-language:subject:subject :user-agent:mime-version:date:date:message-id:received:received :received:received; s=mta-01; t=1664971874; x=1666786275; bh=Yh1 4YdeAHF7vpRcVXwa3NG7XiaY7uA/RQXn1y52glug=; b=llVbk7QF9CXGn3akBGB BJDj+UOcuGVMMEWSp/YZIRanRVJzsCmkIpdcNyLWRssZD/EvlVrTzlVefJ8Hm6TI hvwTfFPIhoKbwY0ugqD6TaLPpA8bbFhiXYHMQTLbbmrmJeG/Thwj+nfgQiy2snAd VeP/umMr4D3KYyUznx9f/wbw= X-Virus-Scanned: amavisd-new at yadro.com Received: from mta-01.yadro.com ([127.0.0.1]) by localhost (mta-01.yadro.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id EiKQp7DzEdgd; Wed, 5 Oct 2022 15:11:14 +0300 (MSK) Received: from T-EXCH-02.corp.yadro.com (T-EXCH-02.corp.yadro.com [172.17.10.102]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by mta-01.yadro.com (Postfix) with ESMTPS id C5E5841221; Wed, 5 Oct 2022 15:11:14 +0300 (MSK) Received: from T-EXCH-08.corp.yadro.com (172.17.11.58) by T-EXCH-02.corp.yadro.com (172.17.10.102) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384) id 15.1.669.32; Wed, 5 Oct 2022 15:11:14 +0300 Received: from [10.199.21.212] (10.199.21.212) by T-EXCH-08.corp.yadro.com (172.17.11.58) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.2.1118.9; Wed, 5 Oct 2022 15:11:13 +0300 Message-ID: <418b8bbb-84d0-7293-42cd-8c552e4357eb@yadro.com> Date: Wed, 5 Oct 2022 15:11:12 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH 2/2] mailbox: Error out early if the mbox driver has failed to submit the message Content-Language: en-US From: Evgeny Shatokhin To: Jassi Brar CC: , Ilya Kuznetsov , References: <20220915164730.515767-1-e.shatokhin@yadro.com> <20220915164730.515767-3-e.shatokhin@yadro.com> <8a378429-ab75-0ebc-a852-24c9d3bb9298@yadro.com> In-Reply-To: <8a378429-ab75-0ebc-a852-24c9d3bb9298@yadro.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.199.21.212] X-ClientProxiedBy: T-EXCH-01.corp.yadro.com (172.17.10.101) To T-EXCH-08.corp.yadro.com (172.17.11.58) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 18.09.2022 19:32, Evgeny Shatokhin wrote: > Thank you for a quick reply! > > On 16.09.2022 20:04, Jassi Brar wrote: >> On Thu, Sep 15, 2022 at 11:50 AM Evgenii Shatokhin >> wrote: >>> >>> mbox_send_message() places the pointer to the message to the queue >>> (add_to_rbuf) then calls msg_submit(chan) to submit the first of the >>> queued messaged to the mailbox. Some of mailbox drivers can return >>> errors from their .send_data() callbacks, e.g., if the message is >>> invalid or there is something wrong with the mailbox device. >>> >> The message can't be invalid because the client code is written for a >> particular provider. > > As of mainline kernel v6.0-rc5, there are mailbox controller drivers > which check if the messages are valid in their .send_data() callbacks. > Example: > > drivers/mailbox/rockchip-mailbox.c, rockchip_mbox_send_data(): >     if (msg->rx_size > mb->buf_size) { >         dev_err(mb->mbox.dev, "Transmit size over buf size(%d)\n", >             mb->buf_size); >         return -EINVAL; >     } > > Other examples are zynqmp_ipi_send_data() from > drivers/mailbox/zynqmp-ipi-mailbox.c, ti_msgmgr_send_data() from > drivers/mailbox/ti-msgmgr.c, etc. > > If this is incorrect and the controller drivers should not do such > things, I'd suggest to clearly state it in the docs, because it is far > from obvious from Documentation/driver-api/mailbox.rst at the moment. > > That is, one could state that checking if the messages to be transmitted > are valid is a responsibility of the callers of mailbox API rather than > of the controller driver. > > I could prepare such patch for the docs. Objections? > >> >> Though it is possible for the mailbox controller to break down for >> some reason. In that case, the blocking api will keep retrying until >> successful. > > As far as I can see from the code, the behaviour seems to be different. > > mbox_send_message() calls msg_submit() to send the message the first > time. If that fails, hrtimer is not armed, so there will be no attempts > to send the message again till tx_out ms pass: > >     err = chan->mbox->ops->send_data(chan, data); >     if (!err) { >         chan->active_req = data; >         chan->msg_count--; >     } > exit: >     spin_unlock_irqrestore(&chan->lock, flags); > >     if (!err && (chan->txdone_method & TXDONE_BY_POLL)) { >         /* kick start the timer immediately to avoid delays */ >         spin_lock_irqsave(&chan->mbox->poll_hrt_lock, flags); >         hrtimer_start(&chan->mbox->poll_hrt, 0, HRTIMER_MODE_REL); >         spin_unlock_irqrestore(&chan->mbox->poll_hrt_lock, flags); >     } > > This is from msg_submit(). Thus, the hrtimer will not fire, tx_tick() > will not be called until tx_out ms have passed, and no attempts to send > the message again will be made here. > > In addition, complete(&chan->tx_complete) will not be called, so, > mbox_send_message() will have to needlessly wait whole tx_out ms. > Only after that, it will call tx_tick(chan, -ETIME), which will, in > turn, call msg_submit() to try to send the message again. If the mbox > has not recovered, sending will fail again. > > Then, mbox_send_message() will exit with -ETIME. The pointer to the > message will remain in chan->msg_data[], but the framework will not > attempt to send it again until the client calls mbox_send_message() for > another, possibly unrelated message. > > In this case, to sum up, mbox_send_message(): > * needlessly waits for tx_out ms; > * only tries to send the message twice rather than makes retries until > successful; > * does not inform the client about the actual error happened, just > returns -ETIME; > * keeps the pointer to the message in chan->msg_data[], which is too > easy to overlook on the client side. Too easy for the client to, say, > reuse the structure and cause trouble. > > What I suggest is to leave it to the client (or some other > provider-specific code using the client) what to do with the failures. > > If the error is reported by the controller driver, don't wait in > mbox_send_message(), just pass the error to the client and exit. If the > client decides to ignore the error - OK, its problem. Or - it may kick > the mbox device somehow in a provider-specific way to make it work, or - > reset the channel, or - do anything else to make things work again. > > The behaviour of mbox_send_message() would then become more consistent: > either it has sent the message successfully or it failed and returned an > error, without side-effects (like the pointer to that message kept in > the internal buffer). > > I do not think this change would break the existing controller drivers > and client drivers. > > What do you think? > >> But ideally the client, upon getting -ETIME, should free() >> and request() the channel reset it (because controller drivers usually >> don't contain the logic to automatically reset upon some error). >> >> thanks. Any updates on this? Looking forward to your comments. Regards, Evgenii