From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Franky Lin" Subject: Re: [PATCH 2/6] brcmfmac: Handling the interrupt in ISR directly for non-OOB Date: Tue, 28 Aug 2012 09:45:39 -0700 Message-ID: <503CF5B3.8040201@broadcom.com> References: <1346063114-30361-1-git-send-email-wni@nvidia.com> <1346063114-30361-3-git-send-email-wni@nvidia.com> <503B9F31.5050502@broadcom.com> <503BD345.6030501@wwwdotorg.org> <1346152413.3516.211.camel@tegra-chromium-2> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1346152413.3516.211.camel@tegra-chromium-2> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Wei Ni Cc: Stephen Warren , Arend van Spriel , "rvossen-dY08KVG/lbpWk0Htik3J/w@public.gmane.org" , Rakesh Kumar , Laxman Dewangan , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "brcm80211-dev-list-dY08KVG/lbpWk0Htik3J/w@public.gmane.org" List-Id: linux-tegra@vger.kernel.org On 08/28/2012 04:13 AM, Wei Ni wrote: > On Tue, 2012-08-28 at 04:06 +0800, Stephen Warren wrote: >> On 08/27/2012 09:24 AM, Arend van Spriel wrote: >>> On 08/27/2012 12:25 PM, Wei Ni wrote: >>>> In case of inband interrupts, if we handle the interrupt in dpc thread, >>>> two level of thread switching takes place to process wifi interrupts. >>>> One in SDHCI driver and the other in Wifi driver. This may cause the >>>> system >>>> instability. >>> >>> Looking into the sdhci/mmc code indeed shows that the brcmfmac irq >>> handler is not called in true IRQ context. So the dpc thread may add >>> unnecessary complexity, but to me there is not indication that there is >>> a stability issue. > > The brcmfmac irq handler is called in the thread sdio_irq_thread(), this > thread indeed is driven by the sdhci irq, although it's not the true IRQ > context. If the brcmfmac doesn't clear the IRQ condition ASAP, the > sdio_irq_thread will be triggered again and again, and in this condition > it's too difficult to run the brcmfmac dpc thread, more and more > interrupt can't be handled. > >>> >>>> Because the SDHCI calls sdio_irq_thread() to handle the irq, this >>>> thread locks >>>> mmc host and calls wifi handler. It expects WiFi handler to be quick and >>>> enables sdio interrupt from card at end. If wifi handler defers this >>>> work for >>>> a different thread, sdio_irq_thread() will be stuck on next wifi >>>> interrupt >>>> since mmc lock is not freed. >>> >>> Not sure if I can follow this explanation. The isr is called with host >>> claimed (by sdio_irq_thread) and all it does is at a linked list member >>> and signal the dpc thread. After doing this the host is released. >> >> Is the issue something like the ISR handler or first level of threading >> does: >> >> * Trigger DPC >> * Re-enable interrupt >> >> So that the interrupt then fires again before the triggered DPC can run >> to handle/clear it, thus causing an interrupt storm? >> >> Whereas handling the interrupt directly prevents this race condition? > > Above is my understanding. > Hi Wei, I understand the issue here and totally agree that we should treat in-band and out-band interrupts differently. But my concern is that the behavior of releasing the host before calling brcmf_sdbrcm_isr and grab it after is likely error prone. Also we are restructuring the dpc routine internally and it's almost done. I will find a better solution for in-band interrupt and get it the queue as well. So I suggest dropping this patch. Thanks, Franky