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. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
