bge(4) one packet wedge

[Oleg Bulyzhin]

On Wed, Aug 23, 2006 at 05:54:24PM -0700, David Christensen wrote:
> > On Wed, Aug 23, 2006 at 12:53:49PM -0700, David Christensen wrote:
> > > This "lost interrupt" type of problem is addressed by the use of the
> > > status_tag 
> > > field in the status block.  (Listed as bge_rsvd0 in the 
> > bge_status_block
> > > structure). 
> > > Everytime the status block is updated a new tag value is 
> > written to the
> > > status block.  
> > > When the ISR starts the driver should record the status_tag 
> > value.  At
> > > the end
> > > of the ISR, the driver should compare the current 
> > status_tag value is
> > > the status
> > > block with the value recorded on entry to the ISR.  If the 
> > values are
> > > the same
> > > then no additional status block updates have occurred so 
> > there shouldn't
> > > be
> > > any packets hanging around.  If the values are different 
> > then additional
> > > packets
> > > or completions are waiting around so the ISR should loop 
> > around again.
> > > At the 
> > > end of the ISR the driver will write the status_tag value it last
> > > handled to a
> > > mailbox register, letting the hardware know the last status 
> > block update
> > > handled.
> > > If necessary the hardware will generate a new interrupt and 
> > start the
> > > process over
> > > again.
> > > 
> > > This entire process should be included in the Linux driver, 
> > I don't see
> > > it being
> > > used in the bge driver (bge_intr()).
> > > 
> > > Dave
> > > 
> > 
> > Could you please answer few questions?
> > 
> > 1) I've found status tag is returned in status block even if 
> > bit 9 of Misc.
> >    Host Control Register is not set, is it ok?
> 
> Which controller are you using?  This bit is reserved on the 5700
> (which didn't support tagged status mode) but all other controllers
> should support it and all of the Broadcom drivers will always
> enable it.

I tested it on bcm5701 & bcm5721

> 
> > 
> > 2) Status tag is returned in bits 0-7 of status tag field of 
> > status block,
> >    as long as i know it should be returned in bits 31-24, is it ok?
> 
> Not sure what you mean by this.  If you're seeing it in bits 31-24
> of the status block then there may be an endian issue on your system.
> Check that byte/word swapping is set correctly.
> 
> > 
> > 3) If i try to return processed tag (at the end of ISR) in 
> > Mailbox 0 register:
> >    CSR_WRITE_4(sc, BGE_MBX_IRQ0_LO, status_tag << 24);
> >    it would lead to disabled interrupts.
> >    I've thought this should not happen cause in_isr bits 
> > (0-23) are cleared.
> 
> Writing a non-zero value to bits 23:0 will cause the interrupt to
> be disabled:
> 
> CSR_WRITE_4(sc, BGE_MBX_IRQ0_LO, 1);
> 
> Writing all zeros to bits 23:0 will enable interrupts.
> 
> CSR_WRITE_4(sc, BGE_MBX_IRQ0_LO, status_tag << 24);
> 
> The tag value written to bits 31:24 does not affect the interrupt
> state.

Yes, this is i'm talking about:
CSR_WRITE_4(sc, BGE_MBX_IRQ0_LO, 0x01000000) would lead to _disabled_
interrupts.
Tested on bcm5701 & bcm5721.

P.S. bcm5705 does not support tagged status mode, am i right?
-- 
Oleg.