Re: Little help with Seabios PV-Drivers for XEN

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

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@bendigoit.com.au> 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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