Re: [Qemu-devel] Data bus error with redeonfb on mips_fulong2e

[Aleksandar Markovic]

Hello, Paul, Zoltan


> From: BALATON Zoltan <address@hidden>
> Subject: Data bus error with redeonfb on mips_fulong2e
> 
> Hello,
> 
> Trying to debug the Linux kernel oops with radeonfb I've added some more
> debug logs and got this:
> 
> radeonfb_pci_register BEGIN
> pci_host_data: pci_data_read: ati-vga: addr=04 val=00000000 len=4
> PCI: Enabling device 0000:00:06.0 (0000 -> 0003)
> pci_host_data: pci_data_read: ati-vga: addr=04 val=00000000 len=4
> pci_host_data: pci_data_write: ati-vga: addr=04 val=00000003 len=4
> pci_update_mappings: adding bar 0 to pci.mem @ 0x14000000
> pci_update_mappings: adding bar 1 to io @ 0x4000
> pci_update_mappings: adding bar 2 to pci.mem @ 0x15050000
> pci_host_data: pci_data_read: ati-vga: addr=3c val=00000000 len=4
> radeonfb_pci_register fb_base_phys=14000000
> radeonfb_pci_register mmio_base_phys=15050000
> radeonfb_pci_register request mem regions
> radeonfb_pci_register map regions
> radeonfb_pci_register mmio_base=9000000015050000
> Data bus error, epc == ffffffff80418e4c, ra == ffffffff80418e4c
> (full oops dump in previous message but I couldn't find anything useful in
> there so omitted here)
>

Paul, Zoltan is experimenting with ATI Radeon support in QEMU. However,
he hits this problem while booting with Linux kernel. May I ask you for
your comments/insight on thi matter? The board that is being emulated
is Fulong 2E (with Loongson 2E CPU).

Zoltan, can you provide here step-by-step repro procedure so that Paul
doesn't need to search other email threads?

Thanks to both for considering my requests.

Aleksandar


> I think the problem is around here (I have to guess because Linux prints
> (ptrval) instead of offsets in oops message as a security measure that I
> don't know how to turn off and the mips64 objdump that comes with my
> distro can't interleave source with disassembly so even if I have the
> offset can't find the source line by it so I had to go by debug printfs):
> 
> linux-4.15.10/drivers/video/fbdev/aty/radeon_base.c:
>     2311         /* Set base addrs */
>     2312         rinfo->fb_base_phys = pci_resource_start (pdev, 0);
>     2313         rinfo->mmio_base_phys = pci_resource_start (pdev, 2);
>     2314         pr_debug("radeonfb_pci_register fb_base_phys=%lx\n", > 
> rinfo->fb_base_phys);
>     2315         pr_debug("radeonfb_pci_register mmio_base_phys=%lx\n", > 
> rinfo->mmio_base_phys);
>     2316
>     2317         /* request the mem regions */
>     2318         pr_debug("radeonfb_pci_register request mem regions\n");
>     2319         ret = pci_request_region(pdev, 0, "radeonfb framebuffer");
>     2320         if (ret < 0) {
>     2321                 printk( KERN_ERR "radeonfb (%s): cannot request > 
> region 0.\n",
>     2322                         pci_name(rinfo->pdev));
>     2323                 goto err_release_fb;
>     2324         }
>     2325
>     2326         ret = pci_request_region(pdev, 2, "radeonfb mmio");
>     2327         if (ret < 0) {
>     2328                 printk( KERN_ERR "radeonfb (%s): cannot request > 
> region 2.\n",
>     2329                         pci_name(rinfo->pdev));
>     2330                 goto err_release_pci0;
>     2331         }
>     2332
>     2333         /* map the regions */
>     2334         pr_debug("radeonfb_pci_register map regions\n");
>     2335         rinfo->mmio_base = ioremap(rinfo->mmio_base_phys, > 
> RADEON_REGSIZE);
>     2336         if (!rinfo->mmio_base) {
>     2337                 printk(KERN_ERR "radeonfb (%s): cannot map MMIO\n",
>     2338                        pci_name(rinfo->pdev));
>     2339                 ret = -EIO;
>     2340                 goto err_release_pci2;
>     2341         }
>     2342         pr_debug("radeonfb_pci_register mmio_base=%px\n", > 
> rinfo->mmio_base);
>     2343
>     2344         rinfo->fb_local_base = INREG(MC_FB_LOCATION) << 16;
>     2345         pr_debug("radeonfb_pci_register fb_local_base=%lx\n", > 
> rinfo->fb_local_base);
> 
> So it fails in INREG on line 2344 which is in radeonfb.h:380
> 
> #define INREG(addr)             readl((rinfo->mmio_base)+addr)
> 
> This reg read never reaches QEMU so either something's wrong with the
> mmio_base or readl can't handle it correctly. This seems to be something
> Linux MIPS specific that I have no idea about. Does this make sense to
> anyone?
> 
> Regards,
> BALATON Zoltan
> 

I appreciate your help!

Aleksandar