Re: [PATCH v2 02/13] dp8393x: Clean up endianness hacks

[Philippe Mathieu-Daudé]

On 1/6/20 11:19 PM, Finn Thain wrote:
> On Fri, 20 Dec 2019, Finn Thain wrote:
>
> > The in_use field is no different to the other words handled using
> > dp8393x_put() and dp8393x_get(). Use the same technique for in_use
> > that is used everywhere else.
> >
> > Signed-off-by: Finn Thain <address@hidden>
> > ---
> > Changed since v1:
> >   - Use existing 'address' variable rather than declare a new one.
> >
> > Laurent tells me that this clean-up has been tried before. He referred
> > me to commit c744cf7879 ("dp8393x: fix dp8393x_receive()") and
> > commit 409b52bfe1 ("net/dp8393x: correctly reset in_use field").
> >
> > Both of those patches look wrong to me because they both pass the wrong
> > byte count to address_space_rw(). It's possible that those patches were
> > needed to work around some kind of bug elsewhere, for example, an
> > off-by-one result from dp8393x_crda(). The preceding patch in this series
> > might help there.
>
> Unfortunately this patch really does break NetBSD/arc 5.1, just as
> Laurent said it would, just as commit c744cf7879 did.
>
> Yet these patches are correct. What gives?
>
> I found that one more change can make guests work (for both m68k q800 and
> mips64el magnum machines) --
>
> --- a/hw/net/dp8393x.c
> +++ b/hw/net/dp8393x.c
> @@ -246,8 +246,10 @@ static void dp8393x_put(dp8393xState *s, int width,
> int offset,
>                           uint16_t val)
>   {
>       if (s->big_endian) {
> +        s->data[offset * width] = 0;
>           s->data[offset * width + width - 1] = cpu_to_be16(val);
>       } else {
> +        s->data[offset * width + width - 1] = 0;
>           s->data[offset * width] = cpu_to_le16(val);
>       }
>   }
>
> For a wide bus interface, this forces the Most Significant Word (MSW) to
> zero. Yet another endianness hack, but it makes NetBSD 5.1 'sn' driver
> happy.

Can you write a list of real word addresses/values/result expected for 
each endianess, so we can add a qtest for this?

> There is a similar issue with the Linux jazzsonic driver. This driver uses
> long-word-sized loads with word-sized MMIO registers --
>
> #define SONIC_READ(reg) (*((volatile unsigned int *)dev->base_addr+reg))
>
> This driver also expects the MSW to be zero. But the MSW actually equals
> the LSW, and the driver fails to probe:
>
> SONIC ethernet controller not found (0x40004)
>
> This seems to indicate that qemu-system-mips64el -M magnum is doing word
> smearing on the processor bus. Does anyone know how to prevent that?

I remember a similar issue with another MIPS board because QEMU doesn't 
model the bus controller, which might do such magic.

> > ---
> >   hw/net/dp8393x.c | 17 ++++++-----------
> >   1 file changed, 6 insertions(+), 11 deletions(-)
> >
> > diff --git a/hw/net/dp8393x.c b/hw/net/dp8393x.c
> > index 1957bd391e..b2cc768d9b 100644
> > --- a/hw/net/dp8393x.c
> > +++ b/hw/net/dp8393x.c
> > @@ -765,8 +765,6 @@ static ssize_t dp8393x_receive(NetClientState *nc, const 
> > uint8_t * buf,
> >           return -1;
> >       }
> >   
> > -    /* XXX: Check byte ordering */
> > -
> >       /* Check for EOL */
> >       if (s->regs[SONIC_LLFA] & SONIC_DESC_EOL) {
> >           /* Are we still in resource exhaustion? */
> > @@ -836,15 +834,12 @@ static ssize_t dp8393x_receive(NetClientState *nc, const 
> > uint8_t * buf,
> >           /* EOL detected */
> >           s->regs[SONIC_ISR] |= SONIC_ISR_RDE;
> >       } else {
> > -        /* Clear in_use, but it is always 16bit wide */
> > -        int offset = dp8393x_crda(s) + sizeof(uint16_t) * 6 * width;
> > -        if (s->big_endian && width == 2) {
> > -            /* we need to adjust the offset of the 16bit field */
> > -            offset += sizeof(uint16_t);
> > -        }
> > -        s->data[0] = 0;
> > -        address_space_rw(&s->as, offset, MEMTXATTRS_UNSPECIFIED,
> > -                         (uint8_t *)s->data, sizeof(uint16_t), 1);
> > +        /* Clear in_use */
> > +        address = dp8393x_crda(s) + sizeof(uint16_t) * 6 * width;
> > +        size = sizeof(uint16_t) * width;
> > +        dp8393x_put(s, width, 0, 0);
> > +        address_space_rw(&s->as, address, MEMTXATTRS_UNSPECIFIED,
> > +                         (uint8_t *)s->data, size, 1);
> >           s->regs[SONIC_CRDA] = s->regs[SONIC_LLFA];
> >           s->regs[SONIC_ISR] |= SONIC_ISR_PKTRX;
> >           s->regs[SONIC_RSC] = (s->regs[SONIC_RSC] & 0xff00) | (((s->regs[SONIC_RSC] 
> > & 0x00ff) + 1) & 0x00ff);