Re: [Xen-devel] Little help with Seabios PV-Drivers for XEN

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Sat, Apr 07, 2012 at 08:01:14PM +0900, Daniel Castro wrote:
> Yes, out of sync, anyway...
> 
> On Fri, Mar 9, 2012 at 8:59 AM, James Harper
> <james.harper@xxxxxxxxxxxxxxxx> wrote:
> >> Hello All,
> >>
> >> I have a little setback with the development of PV Drivers for Xen in 
> >> SeaBIOS.
> >> The initialization code that runs in 32 Bit is working properly.
> >> But, when the system tries to read on the disk I use the ring macros to 
> >> get a
> >> request. The macro usage looks like this:
> >> struct blkif_ring * shared = memalign_low(4096,4096); //return
> >> 0x000fd630 this above 16bit address space SHARED_RING_INIT(shared); So
> >> far I have a pointer located at 0x0009a000 Under 32bit the struct is 
> >> correct
> >> and all is working according to plan.
> >>
> >> But on 16bit operation read on disk I have struct blkfront_info * 
> >> shared_ring
> >> = container_of(op->drive_g.info->shared)); // I get d630 I should get it 
> >> from
> >> the correct segment, but how?
> >> RING_GET_REQUEST(shared_ring); //this returns 0xffff and should be
> >> something 0xa010 segment SS or something like that
> >
> > Just curios, does 16 bit include the required atomic instructions to 
> > manipulate the 32 bit ring counters? Or are you manipulating the ring in 32 
> > bit mode and only accessing the requests already retrieved from the ring in 
> > 16 bit mode?
> This is my current problem, when I do
> RING_GET_REQUEST(GET_GLOBAL(blk_info->private),GET_GLOBAL(blk_info->private->req_prod_pvt));
> The return address is incorrect, so I guess since inside the
> RING_REQUEST MACRO I make memory access I will need to rewrite the
> macro to include the SeaBios macros needed to address 32bit pointers
> in 16bit mode.

Which is
/* Direct access to individual ring elements, by index. */
#define RING_GET_REQUEST(_r, _idx)                                      \
    (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))


?
I would try to not use macros at the start to unravel any
complexity.

Did GET_GLOBAL(blk_info->private) get you a valid pointer? If
you do a hexdump of that area do you get what you expect?

> >
> >> SeaBios has some macros that convert a pointer in 32Bit to 16Bit by 
> >> changing
> >> the segment register, yet I do not know in what segment the ring is 
> >> located,
> >> and the macros are not applied inside the procedure of the macro, for
> >> example:
> >> MAKE_FLATPTR(GET_SEG(SS),RING_GET_REQUEST(shared_ring));
> >> But this will change a 16Bit pointer of segment SS to a 32 bit segment. 
> >> There
> >> is also the reverse but, again I do not know the segment in which I should
> >> look for. Lastly the process inside the macro does not get this benefin, 
> >> and I
> >> do not know if the macro will work with a pointer of size 16bits.
> >>
> >> Any help will be GREATLY appreciated, I am almost done.
> >>
> >
> > I'm not sure if this would be useful, but is there a way to hand over the 
> > ring to the OS PV drivers and avoid the teardown/setup?
> This is before there is an OS. The bios handles the boot process,
> right now I am trying to get the first read on the drive, the boot
> sector.
> >
> > James
> >
> 
> 
> 
> -- 
> +-=====---------------------------+
> | +---------------------------------+ | This space intentionally blank
> for notetaking.
> | |   | Daniel Castro,                |
> | |   | Consultant/Programmer.|
> | |   | U Andes                         |
> +-------------------------------------+
> 
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