linux-kernel - Re: amd5536udc interrupts bug

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Message-ID: <49662C7C.2040500@arcor.de>
Date:	Thu, 08 Jan 2009 17:40:28 +0100
From:	Thomas Dahlmann <dahlmann.thomas@...or.de>
To:	linux-kernel@...r.kernel.org
Subject: Re: amd5536udc interrupts bug

> Vadim Lobanov wrote:
>>  It is my understanding that a handler for a shared interrupt can be
>>  invoked at any time after the corresponding request_irq() call is
>>  made, simply because some other device on the same interrupt may
>>  already be active. This leaves us with a very noticeable race
>>  condition, where udc_irq() can be invoked with uninitialized 'dev'
>>  data.
>
> Yes, your analysis appears correct.

Ah, right. Thanks for your analysis! Never ran into this condition as on the
Geode systems I had the IRQ is shared between UDC and UOC/OTG
(both on the CS5536 chip) and UOC never fires interrupts while UDC
driver is loaded as both drivers (UOC/OTG driver is not in the kernel yet)
register each other which makes sure that interrupts are enabled
after  udc_pci_probe().

>>  more complicated fix may be to try to shuffle all the code around to
>>  make sure that 'dev' is fully initialized before we request the irq,
>>  but I don't understand the code well enough (yet) to comfortably do
>>  this.
>
> Yeah, that's the proper fix.

I could provide a fix within the next weeks. Currently I move to another 
company and
have no hardware to test it.

Maybe you want to try this. It should work to place the register init 
from udc_probe()

/* udc csr registers base */
dev->csr = dev->virt_addr + UDC_CSR_ADDR;
/* dev registers base */
dev->regs = dev->virt_addr + UDC_DEVCFG_ADDR;
/* ep registers base */
dev->ep_regs = dev->virt_addr + UDC_EPREGS_ADDR;
/* fifo's base */
dev->rxfifo = (u32 __iomem *)(dev->virt_addr + UDC_RXFIFO_ADDR);
dev->txfifo = (u32 __iomem *)(dev->virt_addr + UDC_TXFIFO_ADDR);

just before request_irq(...) to allow the interrupt handler to read the 
interrupt status
registers.

Thomas

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