From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 99A9B1292C9 for ; Thu, 21 Mar 2024 15:52:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.184 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711036351; cv=none; b=Bh9mc3yPR5h2cnsbq76qd8aw0F0ZTAW0P42UKEexIm7yrxBhycQ9qQOhGia+nQVOwFRSPnZbocmgGI26C/SIV0AUJRmK4APkdzkcxJqsNrmFBY0+rkcAP+azl7RJ+U0Dv8WS42rwf3+PBROO525ZkxL8zxlYGC8te9HRvzVJTio= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711036351; c=relaxed/simple; bh=vO+59LF2DNwWH2sqIy5zoxEXnKGofXS98o6iGB9I1VA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ayEAOGevtF1PTRPYruEw9obPInFqinQeSAF7yFi0GA0mMCxLWbulBn3UbEcBpAyBr/ue6p+AKY50Gtgdbz3mMYQy7buYQfZ4hfKiDHxxXZIzw6J198V2j1IuGJzUrGjdooYFdr5jtTovr1ZrS6364JGd/JAoPoSSS1J8EhzB0MM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=NOYQ4dW4; arc=none smtp.client-ip=91.218.175.184 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="NOYQ4dW4" Message-ID: <53b2df23-d5ea-498b-a501-b64f753c0074@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1711036347; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2reTOytJMh5foizD5SWaFSRwZSD2WulrWEB+iTZT+JA=; b=NOYQ4dW4Jm1mvANK62WuzMcS2fhb/Cz2mmzJ6a6obOy1x/zCVi9iJrokRVLaSp8ymgicJ1 O6pMTLiEF44xOjsTQyjS+MmwWPUCZNd03HfTM5NOEg2IrOMCX1fxtfG4WlkkRLr97b3OSz rk28k0t9IEvkCpxUQqE2T71VIEfM5Ro= Date: Thu, 21 Mar 2024 11:52:23 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v2 5/8] drm: zynqmp_dp: Don't retrain the link in our IRQ Content-Language: en-US To: Tomi Valkeinen Cc: Michal Simek , David Airlie , linux-kernel@vger.kernel.org, Daniel Vetter , linux-arm-kernel@lists.infradead.org, Laurent Pinchart , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , dri-devel@lists.freedesktop.org References: <20240319225122.3048400-1-sean.anderson@linux.dev> <20240319225122.3048400-6-sean.anderson@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Sean Anderson In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 3/20/24 02:53, Tomi Valkeinen wrote: > On 20/03/2024 00:51, Sean Anderson wrote: >> Retraining the link can take a while, and might involve waiting for >> DPCD reads/writes to complete. This is inappropriate for an IRQ handler. >> Just schedule this work for later completion. This is racy, but will be >> fixed in the next commit. > > You should add the locks first, and use them here, rather than first > adding a buggy commit and fixing it in the next one. I didn't think I could add the locks first since I only noticed the IRQ was threaded right before sending out this series. So yeah, we could add locking, add the workqueue, and then unthread the IRQ. >> Signed-off-by: Sean Anderson >> --- >> Actually, on second look this IRQ is threaded. So why do we have a >> workqueue for HPD events? Maybe we should make it unthreaded? > > Indeed, there's not much work being done in the IRQ handler. I don't know why it's threaded. > > We could move the queued work to be inside the threaded irq handler, > but with a quick look, the HPD work has lines like "msleep(100)" (and > that's inside a for loop...), which is probably not a good thing to do > even in threaded irq handler. > > Although I'm not sure if that code is good to have anywhere. Why do we > even have such code in the HPD work path... We already got the HPD > interrupt. What does "It takes some delay (ex, 100 ~ 500 msec) to get > the HPD signal with some monitors" even mean... The documentation for this bit is | HPD_STATE 0 ro 0x0 Contains the raw state of the HPD pin on the DisplayPort connector. So I think the idea is to perform some debouncing. > Would it be possible to clean up the work funcs a bit (I haven't > looked a the new work func yet), to remove the worst extra sleeps, and > just do all that inside the threaded irq handler? Probably not, since a HPD IRQ results in link retraining, which can take a while. > Do we need to handle interrupts while either delayed work is being done? Probably not. > If we do need a delayed work, would just one work be enough which > handles both HPD_EVENT and HPD_IRQ, instead of two? Maybe, but then we need to determine which pending events we need to handle. I think since we have only two events it will be easier to just have separate workqueues. --Sean