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 X-Spam-Level: X-Spam-Status: No, score=-8.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26BE2C2BA2B for ; Tue, 7 Apr 2020 15:03:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E31D42072A for ; Tue, 7 Apr 2020 15:03:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="dG4Pbiev" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729344AbgDGPDs (ORCPT ); Tue, 7 Apr 2020 11:03:48 -0400 Received: from mail27.static.mailgun.info ([104.130.122.27]:64326 "EHLO mail27.static.mailgun.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729175AbgDGPDs (ORCPT ); Tue, 7 Apr 2020 11:03:48 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1586271827; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: References: Cc: To: Subject: Sender; bh=noVGvGyMDAubVomZ7A9m4ZyJ5BKcZy6LZHICPrl1C/g=; b=dG4PbievOC0eljDzMQX7iFmlHjD+uT24vWQEU/WGvwGdUk4Kf2NF3u47C3GJpDLcWknrDzTj 3XYeHr7obP7xEJfng63tkGWcNrnL6HtY0WLMCAyYYnKEt6QJRpwfv6yLH7/RhA89oZOoHAMQ HV/sL0T1bkWt5UB8/jlBqvkxFpM= X-Mailgun-Sending-Ip: 104.130.122.27 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by mxa.mailgun.org with ESMTP id 5e8c9642.7f1d3ff223b0-smtp-out-n02; Tue, 07 Apr 2020 15:03:30 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id AED5DC433F2; Tue, 7 Apr 2020 15:03:30 +0000 (UTC) Received: from [10.226.58.28] (i-global254.qualcomm.com [199.106.103.254]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: jhugo) by smtp.codeaurora.org (Postfix) with ESMTPSA id 86D1BC433D2; Tue, 7 Apr 2020 15:03:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 86D1BC433D2 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=none smtp.mailfrom=jhugo@codeaurora.org Subject: Re: [PATCH 3/3] bus: mhi: core: Remove link_status() callback To: Manivannan Sadhasivam Cc: hemantk@codeaurora.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org References: <1586207077-22361-1-git-send-email-jhugo@codeaurora.org> <1586207077-22361-4-git-send-email-jhugo@codeaurora.org> <20200407055809.GA2442@Mani-XPS-13-9360> From: Jeffrey Hugo Message-ID: Date: Tue, 7 Apr 2020 09:03:28 -0600 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <20200407055809.GA2442@Mani-XPS-13-9360> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/6/2020 11:58 PM, Manivannan Sadhasivam wrote: > Hi Jeff, > > On Mon, Apr 06, 2020 at 03:04:37PM -0600, Jeffrey Hugo wrote: >> If the MHI core detects invalid data due to a PCI read, it calls into >> the controller via link_status() to double check that the link is infact >> down. All in all, this is pretty pointless, and racy. There are no good >> reasons for this, and only drawbacks. >> >> Its pointless because chances are, the controller is going to do the same >> thing to determine if the link is down - attempt a PCI access and compare >> the result. This does not make the link status decision any smarter. >> >> Its racy because its possible that the link was down at the time of the >> MHI core access, but then recovered before the controller access. In this >> case, the controller will indicate the link is not down, and the MHI core >> will precede to use a bad value as the MHI core does not attempt to retry >> the access. >> >> Retrying the access in the MHI core is a bad idea because again, it is >> racy - what if the link is down again? Furthermore, there may be some >> higher level state associated with the link status, that is now invalid >> because the link went down. >> >> The only reason why the MHI core could see "invalid" data when doing a PCI >> access, that is actually valid, is if the register actually contained the >> PCI spec defined sentinel for an invalid access. In this case, it is >> arguable that the MHI implementation broken, and should be fixed, not >> worked around. >> >> Therefore, remove the link_status() callback before anyone attempts to >> implement it. >> >> Signed-off-by: Jeffrey Hugo > > LGTM. But as per the IRC discussion I'd like the mhi_reg_read() to be > implemented as a callback in mhi_controller struct inorder to truly make MHI > a PCI agnostic bus. > > Since we don't have any controller driver in mainline, I think it is the > good time to do this change. No problem. I thought you might prefer that approach, hence the discussion. :) Do you want that included in this change, or as a follow up? > > For this, > > Reviewed-by: Manivannan Sadhasivam > > Thanks, > Mani > >> --- >> drivers/bus/mhi/core/init.c | 6 ++---- >> drivers/bus/mhi/core/main.c | 5 ++--- >> include/linux/mhi.h | 2 -- >> 3 files changed, 4 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c >> index b38359c..2af08d57 100644 >> --- a/drivers/bus/mhi/core/init.c >> +++ b/drivers/bus/mhi/core/init.c >> @@ -812,10 +812,8 @@ int mhi_register_controller(struct mhi_controller *mhi_cntrl, >> if (!mhi_cntrl) >> return -EINVAL; >> >> - if (!mhi_cntrl->runtime_get || !mhi_cntrl->runtime_put) >> - return -EINVAL; >> - >> - if (!mhi_cntrl->status_cb || !mhi_cntrl->link_status) >> + if (!mhi_cntrl->runtime_get || !mhi_cntrl->runtime_put || >> + !mhi_cntrl->status_cb) >> return -EINVAL; >> >> ret = parse_config(mhi_cntrl, config); >> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c >> index eb4256b..473278b8 100644 >> --- a/drivers/bus/mhi/core/main.c >> +++ b/drivers/bus/mhi/core/main.c >> @@ -20,9 +20,8 @@ int __must_check mhi_read_reg(struct mhi_controller *mhi_cntrl, >> { >> u32 tmp = readl(base + offset); >> >> - /* If there is any unexpected value, query the link status */ >> - if (PCI_INVALID_READ(tmp) && >> - mhi_cntrl->link_status(mhi_cntrl)) >> + /* If the value is invalid, the link is down */ >> + if (PCI_INVALID_READ(tmp)) >> return -EIO; >> >> *out = tmp; >> diff --git a/include/linux/mhi.h b/include/linux/mhi.h >> index ad19960..be704a4 100644 >> --- a/include/linux/mhi.h >> +++ b/include/linux/mhi.h >> @@ -335,7 +335,6 @@ struct mhi_controller_config { >> * @syserr_worker: System error worker >> * @state_event: State change event >> * @status_cb: CB function to notify power states of the device (required) >> - * @link_status: CB function to query link status of the device (required) >> * @wake_get: CB function to assert device wake (optional) >> * @wake_put: CB function to de-assert device wake (optional) >> * @wake_toggle: CB function to assert and de-assert device wake (optional) >> @@ -417,7 +416,6 @@ struct mhi_controller { >> >> void (*status_cb)(struct mhi_controller *mhi_cntrl, >> enum mhi_callback cb); >> - int (*link_status)(struct mhi_controller *mhi_cntrl); >> void (*wake_get)(struct mhi_controller *mhi_cntrl, bool override); >> void (*wake_put)(struct mhi_controller *mhi_cntrl, bool override); >> void (*wake_toggle)(struct mhi_controller *mhi_cntrl); >> -- >> Qualcomm Technologies, Inc. is a member of the >> Code Aurora Forum, a Linux Foundation Collaborative Project. -- Jeffrey Hugo Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.