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 A6B3FC43217 for ; Thu, 1 Dec 2022 20:38:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229777AbiLAUi3 (ORCPT ); Thu, 1 Dec 2022 15:38:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35112 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229692AbiLAUiZ (ORCPT ); Thu, 1 Dec 2022 15:38:25 -0500 Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A72CA13C3 for ; Thu, 1 Dec 2022 12:38:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1669927104; x=1701463104; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=38oa5iNj8+pu7Dm8hMinaLo5Pj+hXioLhzHtZupPIes=; b=YtQSPoc/qvEhRdHG+HA+v860UvB0LyQsZVwrO/kQNfmJXWmVHXXsgjE2 X/HSf8b2GZa1ugaBnwIdlf9vFfnZvPYTvIWixBAc0gfVz8VtQmgPojIyT oNNUu+c672eDhOMXyIbhWhegL+5P7U8Gr1PxGRFtg1BSd/6BLRxNxloKB 9LNkupBOAojZCA7BpEIFAnvWrED/2L6ARrimlIWccQEMyJx8tLAZmxJ6n dPyQg9QXPbEsCrUczwZFcMDBiLX6YPeB+9TRP4X1g+nV0w3pcA6SRkviP TBfWTOWib5Pkji3nzphNIV4QIN7FXMzK/V+oyDD8H9GU32DOubpyFFfev g==; X-IronPort-AV: E=McAfee;i="6500,9779,10548"; a="314498377" X-IronPort-AV: E=Sophos;i="5.96,210,1665471600"; d="scan'208";a="314498377" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Dec 2022 12:38:05 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10548"; a="644781661" X-IronPort-AV: E=Sophos;i="5.96,210,1665471600"; d="scan'208";a="644781661" Received: from twcarol-mobl.amr.corp.intel.com (HELO [10.212.10.40]) ([10.212.10.40]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Dec 2022 12:38:04 -0800 Message-ID: Date: Thu, 1 Dec 2022 12:12:48 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.4.2 Subject: Re: [PATCH 2/3] soundwire: cadence: Remove wasted space in response_buf Content-Language: en-US To: Richard Fitzgerald , vkoul@kernel.org Cc: yung-chuan.liao@linux.intel.com, sanyog.r.kale@intel.com, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, patches@opensource.cirrus.com References: <20221201134845.4055907-1-rf@opensource.cirrus.com> <20221201134845.4055907-3-rf@opensource.cirrus.com> From: Pierre-Louis Bossart In-Reply-To: <20221201134845.4055907-3-rf@opensource.cirrus.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/1/22 07:48, Richard Fitzgerald wrote: > The response_buf was declared much larger (128 entries) than the number > of responses that could ever be written into it (maximum 8). Indeed I don't know why we used 128 entries. This is a magic value that doesn't appear in any specs I've looked at. Note that there's 'sniffer' mode when each response takes two consecutive 32-words in the FIFO. we've never used this mode though so it's not really an issue. It's also possible that this is related to the automatic command retry, where a failed command can be re-issued 15 times. However in that case the worst case would be 32 commands * 15 = 480. The value of 128 makes no sense at all, unless it was an upper bound for 8 * 15. We don't use this hardware retry btw. See more below... > Reduce response_buf to 8 entries and add checking in cdns_read_response() > to prevent overflowing reponse_buf if CDNS_MCP_RX_FIFO_AVAIL contains > an unexpectedly large number. > > Signed-off-by: Richard Fitzgerald > --- > drivers/soundwire/cadence_master.c | 6 ++++++ > drivers/soundwire/cadence_master.h | 2 +- > 2 files changed, 7 insertions(+), 1 deletion(-) > > diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c > index 27699f341f2c..95c84d9f0775 100644 > --- a/drivers/soundwire/cadence_master.c > +++ b/drivers/soundwire/cadence_master.c > @@ -774,8 +774,14 @@ static void cdns_read_response(struct sdw_cdns *cdns) > u32 num_resp, cmd_base; > int i; > > + BUILD_BUG_ON(ARRAY_SIZE(cdns->response_buf) < CDNS_MCP_CMD_LEN); > + > num_resp = cdns_readl(cdns, CDNS_MCP_FIFOSTAT); > num_resp &= CDNS_MCP_RX_FIFO_AVAIL; > + if (num_resp > ARRAY_SIZE(cdns->response_buf)) { > + dev_warn(cdns->dev, "RX AVAIL %d too long\n", num_resp); > + num_resp = CDNS_MCP_CMD_LEN; .... this is different from what the hardware documentation tells me. The range of values to RX_FIFO_AVAIL is 0..RX_FIFO_DEPTH + 2. I don't understand the +2, but we should maybe be more cautious and use u32 response_buf[CDNS_MCP_CMD_LEN + 2]; > + } > > cmd_base = CDNS_MCP_CMD_BASE; > > diff --git a/drivers/soundwire/cadence_master.h b/drivers/soundwire/cadence_master.h > index 0434d70d4b1f..c2d817e8e22a 100644 > --- a/drivers/soundwire/cadence_master.h > +++ b/drivers/soundwire/cadence_master.h > @@ -117,7 +117,7 @@ struct sdw_cdns { > struct sdw_bus bus; > unsigned int instance; > > - u32 response_buf[0x80]; > + u32 response_buf[8]; > struct completion tx_complete; > struct sdw_defer *defer; >