Re: [Qemu-devel] [PATCH v2] qtest: ask endianness of the target in qtest_init()

[David Gibson]

On Mon, Oct 10, 2016 at 03:10:33PM +0100, Peter Maydell wrote:
> On 10 October 2016 at 14:39, David Gibson <address@hidden> wrote:
> > In the overwhelming majority of cases the endianness of the device is
> > known independent of the guest CPU and board.
> 
> We don't seem to model things that way:
> 
> $ git grep '.endianness = DEVICE_NATIVE' |wc -l
> 341
> $ git grep '.endianness = DEVICE_BIG' |wc -l
> 18
> $ git grep '.endianness = DEVICE_LITTLE' |wc -l
> 172

Sigh.  So, most of these are themselves mistakes.

A lot of these are target specific devices that should be tagged with
their target's (notional) endianness, rather than NATIVE.  That
covers:

ARM
        hw/arm                                           68
        hw/*/bcm283*                                      8
        hw/*/imx*                                        13
        hw/*/omap*                                       27
        hw/*/pl*                                         10
        hw/*/exynos*                                      8
        hw/net/lan9118.c                                  2
        hw/*/pxa2xx*                                      8
        hw/gpio/zaurus.c                                  1
        hw/*/versatile*                                   3
        hw/*/allwinner*                                   3
        hw/*/arm*                                        15
        hw/*/a9*                                          3
        hw/char/cadence*                                  2
        hw/*/digic*                                       2
        hw/*/stm32f2xx*                                   5
        hw/usb/tusb6010.c                                 1
        hw/misc/mst_fpga.c                                1
        hw/net/smc91c111.c                                1
        hw/net/stellaris_enet.c                           1
        hw/misc/zynq*                                     2
        hw/dma/xlnx_dpdma.c                               1
        hw/display/xlnx_dp.c                              4
        hw/ssi/xilinx_spips.c                             1
        hw/display/tc6393xb.c                             1
        hw/audio/marvell_88w8618.c                        1
        hw/block/onenand.c                                1
                                                        ---
                TOTAL                                   193                     
                

CRIS
        hw/cris                                           2
        hw/*/etraxfs*                                     3
                                                        ---
                TOTAL                                     5

LM32
        hw/*/milkymist*                                  10
        hw/*/lm32*                                        2
                                                        ---
                TOTAL                                    12                     
                                 

M68K
        hw/m68k                                           4
        hw/*/mcf*                                         2
                                                        ---
                TOTAL                                     6

MICROBLAZE
        hw/dma/xilinx_axidma.c                            1
        hw/char/xilinx_uartlite.c                         1
        hw/intc/xilinx_intc.c                             1
        hw/net/xilinx_ethlite.c                           1
        hw/timer/xilinx_timer.c                           1
        hw/ssi/xilinx_spi.c                               1
                                                        ---
                TOTAL                                     6

MIPS
        hw/mips                                           8
        hw/*/mips*                                        5
        hw/display/jazz_led.c                             1
        hw/dma/rc4030.c                                   2
        hw/net/dp8393x.c                                  1
        hw/pci-host/bonito.c                              5
                                                        ---
                TOTAL                                    22

OPENRISC
        hw/openrisc                                       1

PPC
        hw/ppc                                            7
        hw/char/escc.c                                    1
        hw/ide/macio.c                                    1
        hw/misc/macio/cuda.c                              1
        hw/misc/applesmc.c                                2
        hw/net/fsl_etsec/etsec.c                          1
                                                        ---
                TOTAL                                    13

SH
        hw/sh4                                            4
        hw/*/sh_*                                         3
        hw/display/sm501.c                                4
                                                        ---
                TOTAL                                    11

SPARC
        hw/*/grlib*                                       3
        hw/*/slavio*                                     11
        hw/dma/sparc32_dma.c                              1
        hw/dma/sun4m_iommu.c                              1
        hw/display/tcx.c                                  7
        hw/pci-host/apb.c                                 2
        hw/misc/eccmemctl.c                               2
        hw/display/cg3.c                                  1
        hw/audio/cs4231.c                                 1
                                                        ---
                TOTAL                                    29

UNICORE32
        hw/*/puv3*                                        5

X86
        hw/i386                                           9
        hw/pci-host/q35.c                                 1
        hw/timer/hpet.c                                   1
                                                        ---
                TOTAL                                    11
        
XTENSA
        hw/xtensa                                         3


                                                        ===
                        OVERALL TOTAL                   317

There are some PCI devices, where AFAICT, the NATIVE_ENDIAN tag is
Just Plain Wrong (i.e. I believe these devices will be broken on BE
targets):
        hw/scsi/lsi53c895a.c                             3
        hw/ipack/tpci200.c                               5
        hw/misc/edu.c                                    1
        hw/audio/intel-hda.c                             1
        hw/pci/pcie_host.c                               1

And there are some devices which only accept 1 byte accesses, so the
endianness is irrelevant anyway:
        hw/block/fdc.c                                   2
        hw/dma/i8257.c                                   2
        hw/isa/vt82c686.c                                1

There are ISA devices.  I'd expect these to be always-LE, but I'm not
sure exactly how they're handled.  In wonder if they've been tested on
BE.
        hw/char/parallel.c                               1
        hw/input/pckbd.c                                 1
        hw/display/vga-isa-mm.c                          1

Then there are some which are part of the MR infrastructure, rather
than a device itself:
        exec.c                                           8
        ioport.c                                         1
        memory.c                                         1
        include/exec/cpu-common.h                        1
        hw/core/empty_slot.c                             1


What does that leave..

        hw/block/pflash_cfi01.c                         1
        hw/block/pflash_cfi02.c                         2

These appear to have its own internal endianness handling

        hw/char/serial.c                                2
        hw/timer/m48t59.c                               1

These are "raw" MMIO devices which are common enough that they do
exist in the wild with weird wiring variations.  These were always
going to require some special casing.

        hw/intc/apic.c                                  1
        hw/intc/ioapic.c                                1

All the platforms which have APIC (x86 & arm) are notionally LE.  I
imagine it would break if you tried to attach it to a BE platform.

        hw/net/lance.c                                  1

This is the backend of the old PC-Net driver.  I suspect the "wrapper"
layers by which it's usually used may fix the endianness.  Or possibly
it's just broken on BE.

        hw/scsi/esp.c                                   1

The platforms it appears on (MIPS Jazz & sun4m) are both notionally
BE. I imagine it would break if you tried to attach it to an LE
platform.

And finally
        hw/misc/ivshmem.c                               1
        hw/virtio/virtio-mmio.c                         1
        hw/xen/xen_pt*                                  2

virtio has been discussed before.  The others are also purely virtual
devices, which I suspect have made the same design error as old
virtio.  However I don't think any BE platforms use ivshmem or xen in
practice, so they could be considered always-LE.


So, yeah, I still think "overwhelming majority" is accurate.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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