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 930DDC433F5 for ; Thu, 6 Oct 2022 03:07:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230044AbiJFDHY (ORCPT ); Wed, 5 Oct 2022 23:07:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58206 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229924AbiJFDHT (ORCPT ); Wed, 5 Oct 2022 23:07:19 -0400 Received: from wout4-smtp.messagingengine.com (wout4-smtp.messagingengine.com [64.147.123.20]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9F43280EB9 for ; Wed, 5 Oct 2022 20:07:16 -0700 (PDT) Received: from compute3.internal (compute3.nyi.internal [10.202.2.43]) by mailout.west.internal (Postfix) with ESMTP id 50B1632009B7; Wed, 5 Oct 2022 23:07:13 -0400 (EDT) Received: from imap50 ([10.202.2.100]) by compute3.internal (MEProxy); Wed, 05 Oct 2022 23:07:14 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=aj.id.au; h=cc :cc:content-type:date:date:from:from:in-reply-to:in-reply-to :message-id:mime-version:references:reply-to:sender:subject :subject:to:to; s=fm1; t=1665025632; x=1665112032; bh=D2A7KGl6Nx Nqwykh+AYiSj2aZjrv6WwosJ3tBKEWL9A=; b=UNh8dCTbt11+Y04xRIMeIQg+Q1 6IS109m/KEqCRXHJZ0D0fapKfJagnxilV4OlZwYfLXpqbyfFU1PmALyDrlVI4jec +P0GaakUCl7jou5ZjBPx84ofanOdmTACKpOXf1i+s9tbxJumaVDWvNoGxDppxREM 8kK7ydXJA2EoPRmk1R/tGvKj3hU8iA6iGSuTjg+855soTewPwltgKq+PwSKRqwOI ZC3mD62TvlMZeppksWRN0iCViyAP4WUTwuUugcJqmuvgJ1EyWEwwpyEyWprmth0L jwROxznY51PGj8OCWGh5iy4GSy220RKmN9qXANbZkNnjVhHERLe+g8jCxP6g== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-type:date:date:feedback-id :feedback-id:from:from:in-reply-to:in-reply-to:message-id :mime-version:references:reply-to:sender:subject:subject:to:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm2; t=1665025632; x=1665112032; bh=D2A7KGl6NxNqwykh+AYiSj2aZjrv 6WwosJ3tBKEWL9A=; b=s6v8JOKhc6PogwG6nV+k5ipmlROWpjI5vzgQgqABWzAV AnJnbYVatK3HYrgyuDABlSjKK/s9ZkRq637ehv7szSZ5A3qD28RO5OcnK5ruOUeB /hLS7Iaff7ZVntV9AVYtXUs8buBgjUH4Rn2SKTdUeBEXGWi/GQlBUU4pLUdp7pVH 7hTg+9S2eVOv5zpgrKJYC+Njlf1euCpgdqWONCyeSI1inkMXuIjZ0zOdbDEdgp0j STEuthh4M2u3MG8ZfmQh1tF/i9McO7sfijfz35Ze713GRJWavYhSOR2h3YVLqvf7 5YdFaA01uy0XMtuRM9wnuGx0QqpMRtkUcSzlYinJbA== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvfedrfeeigedgieekucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepofgfggfkjghffffhvfevufgtsehttdertderredtnecuhfhrohhmpedftehn ughrvgifucflvghffhgvrhihfdcuoegrnhgurhgvfiesrghjrdhiugdrrghuqeenucggtf frrghtthgvrhhnpeekvdekjeekgfejudffteetgeejkeetteduvedtffdtledutdfhheev feetkeeiteenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhroh hmpegrnhgurhgvfiesrghjrdhiugdrrghu X-ME-Proxy: Feedback-ID: idfb84289:Fastmail Received: by mailuser.nyi.internal (Postfix, from userid 501) id 58DF01700083; Wed, 5 Oct 2022 23:07:12 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.7.0-alpha0-1015-gaf7d526680-fm-20220929.001-gaf7d5266 Mime-Version: 1.0 Message-Id: In-Reply-To: References: <20220812144741.240315-1-andrew@aj.id.au> Date: Thu, 06 Oct 2022 13:36:51 +1030 From: "Andrew Jeffery" To: "Joel Stanley" Cc: openipmi-developer@lists.sourceforge.net, "Corey Minyard" , linux-arm-kernel@lists.infradead.org, linux-aspeed@lists.ozlabs.org, linux-kernel@vger.kernel.org, openbmc@lists.ozlabs.org Subject: Re: [PATCH] ipmi: kcs: Poll OBF briefly to reduce OBE latency Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 6 Oct 2022, at 10:20, Joel Stanley wrote: > On Fri, 12 Aug 2022 at 14:48, Andrew Jeffery wrote: >> >> The ASPEED KCS devices don't provide a BMC-side interrupt for the host >> reading the output data register (ODR). The act of the host reading ODR >> clears the output buffer full (OBF) flag in the status register (STR), >> informing the BMC it can transmit a subsequent byte. >> >> On the BMC side the KCS client must enable the OBE event *and* perform a >> subsequent read of STR anyway to avoid races - the polling provides a >> window for the host to read ODR if data was freshly written while >> minimising BMC-side latency. >> > > Fixes...? Is it a fix though? It's definitely an *improvement* in behaviour, but the existing behaviour also wasn't *incorrect*, just kinda unfortunate under certain timings? Dunno. I'm probably splitting hairs. In any case, if we do want a fixes line: Fixes: 28651e6c4237 ("ipmi: kcs_bmc: Allow clients to control KCS IRQ state") > >> Signed-off-by: Andrew Jeffery > > Reviewed-by: Joel Stanley Thanks! > >> --- >> drivers/char/ipmi/kcs_bmc_aspeed.c | 24 +++++++++++++++++++++--- >> 1 file changed, 21 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/char/ipmi/kcs_bmc_aspeed.c b/drivers/char/ipmi/kcs_bmc_aspeed.c >> index cdc88cde1e9a..417e5a3ccfae 100644 >> --- a/drivers/char/ipmi/kcs_bmc_aspeed.c >> +++ b/drivers/char/ipmi/kcs_bmc_aspeed.c >> @@ -399,13 +399,31 @@ static void aspeed_kcs_check_obe(struct timer_list *timer) >> static void aspeed_kcs_irq_mask_update(struct kcs_bmc_device *kcs_bmc, u8 mask, u8 state) >> { >> struct aspeed_kcs_bmc *priv = to_aspeed_kcs_bmc(kcs_bmc); >> + int rc; >> + u8 str; > > str is status, it would be good to spell that out in full. I guess if it trips enough people up we can rename it later. > >> >> /* We don't have an OBE IRQ, emulate it */ >> if (mask & KCS_BMC_EVENT_TYPE_OBE) { >> - if (KCS_BMC_EVENT_TYPE_OBE & state) >> - mod_timer(&priv->obe.timer, jiffies + OBE_POLL_PERIOD); >> - else >> + if (KCS_BMC_EVENT_TYPE_OBE & state) { >> + /* >> + * Given we don't have an OBE IRQ, delay by polling briefly to see if we can >> + * observe such an event before returning to the caller. This is not >> + * incorrect because OBF may have already become clear before enabling the >> + * IRQ if we had one, under which circumstance no event will be propagated >> + * anyway. >> + * >> + * The onus is on the client to perform a race-free check that it hasn't >> + * missed the event. >> + */ >> + rc = read_poll_timeout_atomic(aspeed_kcs_inb, str, >> + !(str & KCS_BMC_STR_OBF), 1, 100, false, >> + &priv->kcs_bmc, priv->kcs_bmc.ioreg.str); >> + /* Time for the slow path? */ > > The mod_timer is the slow path? The question mark threw me. Yeah, mod_timer() is the slow path; read_poll_timeout_atomic() is the fast path and we've exhausted the time we're willing to wait there if we get -ETIMEDOUT. The comment was intended as a description for the question posed by the condition. It made sense in my head but maybe it's confusing more than it is enlightening? Andrew > >> + if (rc == -ETIMEDOUT) >> + mod_timer(&priv->obe.timer, jiffies + OBE_POLL_PERIOD); >> + } else { >> del_timer(&priv->obe.timer); >> + } >> } >> >> if (mask & KCS_BMC_EVENT_TYPE_IBF) { >> -- >> 2.34.1 >>