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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 17AF6C433ED for ; Thu, 20 May 2021 22:39:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E9C9A613AF for ; Thu, 20 May 2021 22:39:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231686AbhETWkm (ORCPT ); Thu, 20 May 2021 18:40:42 -0400 Received: from m43-7.mailgun.net ([69.72.43.7]:46283 "EHLO m43-7.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231653AbhETWkl (ORCPT ); Thu, 20 May 2021 18:40:41 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1621550359; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=u5Fv69WG7AZKBChnOzRtJI8AUhfjpxnX1Q0kHh77Ii0=; b=jXQdWhRjhusmvyahDawM1WP7ln1cKYv8YwI6DU09XbivyJkbiarKLCf8weXBl4pWPMFgZGu0 Ses40pxogBYfS8I0tnFtUibPRB4afRELJWPHD8udgkQ3KslPAIRwt/SF+GqL35GTT5FR+u0k kGQmop+8iNeF55kcS57DYcFgJTY= X-Mailgun-Sending-Ip: 69.72.43.7 X-Mailgun-Sid: WyI1MzIzYiIsICJsaW51eC1hcm0tbXNtQHZnZXIua2VybmVsLm9yZyIsICJiZTllNGEiXQ== Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n02.prod.us-west-2.postgun.com with SMTP id 60a6e50f7b9a7a2b6cb64564 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Thu, 20 May 2021 22:39:11 GMT Sender: khsieh=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 7377FC43460; Thu, 20 May 2021 22:39:11 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: khsieh) by smtp.codeaurora.org (Postfix) with ESMTPSA id D27A4C433F1; Thu, 20 May 2021 22:39:09 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 20 May 2021 15:39:09 -0700 From: khsieh@codeaurora.org To: Stephen Boyd Cc: agross@kernel.org, bjorn.andersson@linaro.org, robdclark@gmail.com, sean@poorly.run, vkoul@kernel.org, abhinavk@codeaurora.org, aravindh@codeaurora.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 1/2] drm/msm/dp: handle irq_hpd with sink_count = 0 correctly In-Reply-To: References: <1621013713-6860-1-git-send-email-khsieh@codeaurora.org> Message-ID: <5d341df202facb3240a72cfb35e18167@codeaurora.org> X-Sender: khsieh@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On 2021-05-20 14:28, Stephen Boyd wrote: > Quoting khsieh@codeaurora.org (2021-05-20 13:05:48) >> On 2021-05-20 12:28, Stephen Boyd wrote: >> >> Put dongle to D3 state so that it will not issue the unnecessary >> >> second >> >> irq_hpd with sink_count = 0. this will prevent the annoy but unharmful >> >> DP_LINK_STATUS_UPDATED warning message. >> >> Again, we can not disable hpd interrupt since dongle still attached >> >> and >> >> hdmi cable can be plugged in at any instant. >> >> >> > >> > Right I'm not suggesting to disable hpd interrupt, just the hpd_irq >> > interrupt once an unplug irq comes in, and do that in hardirq context. >> > Also, I'm suggesting that we consider unplug as a higher priority if >> > the >> > hard irq handler is delayed for some reason and both an unplug irq and >> > an hpd irq are pending in the hardware when the hard irq handler is >> > running. Putting the dongle into D3 state won't fix these problems. >> >> >> >> The unplug interrupt is not happen in this case since dongle still >> attached. >> The unplug interrupt only happen when dongle unplugged. > > Agreed. > >> >> I think you mistakenly think DP_LINK_STATUS_UPDATED is caused by >> unplug >> interrupt. > > Ok, got it. > >> DP_LINK_STATUS_UPDATED happen is due to dongle issue two consecutive >> irq_hpd with sink_count = 0 when hdmi cable unplugged from dongle. >> The first irq_hpd with sink_count = 0 is handled as expected to turn >> off >> display. >> After that the second irq_hpd with sink_count = 0 is handled. >> Since display had turned off, then there is nothing to do but spill >> DP_LINK_STATUS_UPDATED warning message. >> There is no unplug (hpd become low) happen in this case since dongle >> still attached. > > Agreed. > >> >> All interrupt (plug/irq_hpd and unplug) are required to be handled in >> the order of happening. >> We can not ignore any one. >> For example, you plug/unplug two different resolution monitor >> alternative to/from dongle and unplug dongle once for while. >> >> I think the race condition you describe here all had been taken care >> with >> 1) convert irq into event and store at event q in order. >> 2) irq handled base on transaction. Next irq can be handled when >> previous irq transaction is done. >> > > I'm mostly trying to point out that the irq handling and masking needs > to be done in the hard irq context and not in the kthread. It may or > may > not be related to this message that's printed. > > What happens if the hardirq is blocked by some other irq that takes a > long time to process? Imagine this scenario: > > CPU0 CPU1 > ---- ---- > really_long_other_hardirq() { > hpd_irq > hpd_irq > hpd low > } > > dp_display_irq_handler() { > > > } > > Shouldn't we ignore any hpd_irq events in this scenario? And shouldn't > we be disabling the hpd_irq by masking it with DP_DP_IRQ_HPD_INT_MASK > when hpd goes low (i.e. DP_DP_HPD_UNPLUG_INT_MASK)? 1) irq_hpd interrupt always happen before unplug interrupt 2)if hdp_isr_status = (DP_DP_IRQ_HPD_INT_MASK | DP_DP_HPD_UNPLUG_INT_MASK) at the time when read at dp_display_irq_handler(), then DP_DP_IRQ_HPD_INT_MASK will be add into evetn q first followed by DP_DP_HPD_UNPLUG_INT_MASK be add into event q. So that DP_DP_IRQ_HPD_INT_MASK will be executed by the event thread before DP_DP_HPD_UNPLUG_INT_MASK. On the other word, IRQ_HPD has higher priority over UNPLUG in the timing matter. By doing that we can shut down display gracefully. If you insist, at hdp_isr_status = (DP_DP_IRQ_HPD_INT_MASK | DP_DP_HPD_UNPLUG_INT_MASK) case, we can have only add DP_DP_HPD_UNPLUG_INT_MASK to event q only by dropping DP_DP_IRQ_HPD_INT_MASK. Is this will work for you?