Re: [PATCH-for-9.2? v2 1/2] hw/display/vga: Do not reset 'big_endian_fb' in vga_common_reset()

[Benjamin Herrenschmidt]

It's been a long time, I only have vague memories of this :-) But I
think it should be ok.

It does definitely make sense in the virtio case and similar where
the property is set once for the instance.

For bochs and ati, there's a register to configure it as well, so there
*may* be an expectation that it gets reset there, I'm less certain.

So tentatively...

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>


On Mon, 2024-12-02 at 20:48 +0100, Philippe Mathieu-Daudé wrote:
> ping?
> 
> On 29/11/24 11:17, Philippe Mathieu-Daudé wrote:
> > The 'pci-vga' device allow setting a 'big-endian-framebuffer'
> > property since commit 3c2784fc864 ("vga: Expose framebuffer
> > byteorder as a QOM property"). Similarly, the 'virtio-vga'
> > device since commit 8be61ce2ce3 ("virtio-vga: implement
> > big-endian-framebuffer property").
> > 
> > Both call vga_common_reset() in their reset handler, respectively
> > pci_secondary_vga_reset() and virtio_vga_base_reset_hold(), which
> > reset 'big_endian_fb', overwritting the property. This is not
> > correct: the hardware is expected to keep its configured
> > endianness during resets.
> > 
> > Move 'big_endian_fb' assignment from vga_common_reset() to
> > vga_common_init() which is called once when the common VGA state
> > is initialized.
> > 
> > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> > ---
> >   hw/display/vga.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/hw/display/vga.c b/hw/display/vga.c
> > index 892fedc8dce..b074b58c90d 100644
> > --- a/hw/display/vga.c
> > +++ b/hw/display/vga.c
> > @@ -1873,7 +1873,6 @@ void vga_common_reset(VGACommonState *s)
> >       s->cursor_start = 0;
> >       s->cursor_end = 0;
> >       s->cursor_offset = 0;
> > -    s->big_endian_fb = s->default_endian_fb;
> >       memset(s->invalidated_y_table, '\0', sizeof(s-
> > >invalidated_y_table));
> >       memset(s->last_palette, '\0', sizeof(s->last_palette));
> >       memset(s->last_ch_attr, '\0', sizeof(s->last_ch_attr));
> > @@ -2266,6 +2265,7 @@ bool vga_common_init(VGACommonState *s,
> > Object *obj, Error **errp)
> >        * all target endian dependencies from this file.
> >        */
> >       s->default_endian_fb = target_words_bigendian();
> > +    s->big_endian_fb = s->default_endian_fb;
> >   
> >       vga_dirty_log_start(s);
> >