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Date: Thu, 8 May 2014 03:42:59 +0000
From: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>
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Subject: Re: [Qemu-devel] [PATCH v1 4/5] xilinx_timer: Fix writes into TCSR
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To: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Cc: "qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>, linux@roeck-us.net

On Thu, May 08, 2014 at 12:45:03PM +1000, Peter Crosthwaite wrote:
> On Thu, May 8, 2014 at 11:35 AM, Edgar E. Iglesias
> <edgar.iglesias@gmail.com> wrote:
> > From: Guenter Roeck <linux@roeck-us.net>
> >
> > The TCSR register has only 11 valid bits. This is now used by the
> > linux kernel to auto-detect endianness, and causes Linux 3.15-rc1
> > and later to hang when run under qemu-microblaze. Mask valid bits
> > before writing the register to solve the problem.
> >
> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > Reviewed-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
> > Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
> > ---
> >  hw/timer/xilinx_timer.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/hw/timer/xilinx_timer.c b/hw/timer/xilinx_timer.c
> > index 6113b97..3ff1da9 100644
> > --- a/hw/timer/xilinx_timer.c
> > +++ b/hw/timer/xilinx_timer.c
> > @@ -169,7 +169,7 @@ timer_write(void *opaque, hwaddr addr,
> >              if (value & TCSR_TINT)
> >                  value &= ~TCSR_TINT;
> >
> > -            xt->regs[addr] = value;
> > +            xt->regs[addr] = value & 0x7ff;
> 
> In at least the later TRMs, Bit 11 is validly defined as the cascade
> bit, taking the total number of bits to 12. I think this mask should
> be 0xfff.

Hi,

For timer versions without cascading support, bit 11 is reserved.
I think the patch is good. Once someone adds cascading support we
can expose and implement the cascading bit + the necessary
additional regs.

Cheers,
Edgar