From: Wei Hu <weh@xxxxxxxxxxxxx> Sent: Tuesday, August 27, 2019 4:25 AM
>
> Without deferred IO support, hyperv_fb driver informs the host to refresh
> the entire guest frame buffer at fixed rate, e.g. at 20Hz, no matter there
> is screen update or not. This patch supports deferred IO for screens in
> graphics mode and also enables the frame buffer on-demand refresh. The
> highest refresh rate is still set at 20Hz.
>
> Currently Hyper-V only takes a physical address from guest as the starting
> address of frame buffer. This implies the guest must allocate contiguous
> physical memory for frame buffer. In addition, Hyper-V Gen 2 VMs only
> accept address from MMIO region as frame buffer address. Due to these
> limitations on Hyper-V host, we keep a shadow copy of frame buffer
> in the guest. This means one more copy of the dirty rectangle inside
> guest when doing the on-demand refresh. This can be optimized in the
> future with help from host. For now the host performance gain from deferred
> IO outweighs the shadow copy impact in the guest.
>
> v2: Incorporated review comments from Michael Kelley
> - Increased dirty rectangle by one row in deferred IO case when sending
> to Hyper-V.
> - Corrected the dirty rectangle size in the text mode.
> - Added more comments.
> - Other minor code cleanups.
Version history should go after the "---" below so it is not included in
the commit message.
>
> Signed-off-by: Wei Hu <weh@xxxxxxxxxxxxx>
> ---
> drivers/video/fbdev/Kconfig | 1 +
> drivers/video/fbdev/hyperv_fb.c | 221 +++++++++++++++++++++++++++++---
> 2 files changed, 202 insertions(+), 20 deletions(-)
>
> +/* Deferred IO callback */
> +static void synthvid_deferred_io(struct fb_info *p,
> + struct list_head *pagelist)
> +{
> + struct hvfb_par *par = p->par;
> + struct page *page;
> + unsigned long start, end;
> + int y1, y2, miny, maxy;
> + unsigned long flags;
> +
> + miny = INT_MAX;
> + maxy = 0;
> +
> + /*
> + * Merge dirty pages. It is possible that last page cross
> + * over the end of frame buffer row yres. This is taken care of
> + * in synthvid_update function by clamping the y2
> + * value to yres.
> + */
> + list_for_each_entry(page, pagelist, lru) {
> + start = page->index << PAGE_SHIFT;
> + end = start + PAGE_SIZE - 1;
> + y1 = start / p->fix.line_length;
> + y2 = end / p->fix.line_length;
> + if (y2 > p->var.yres)
> + y2 = p->var.yres;
The above test seems contradictory to the comment that
says the clamping is done in synthvid_update(). Also, since
the above calculation of y2 is "inclusive", the clamping should
be done to yres - 1 in order to continue to be inclusive. Then
when maxy + 1 is passed to synthvid_update() everything works
out correctly.
> + miny = min_t(int, miny, y1);
> + maxy = max_t(int, maxy, y2);
> +
> + /* Copy from dio space to mmio address */
> + if (par->fb_ready) {
> + spin_lock_irqsave(&par->docopy_lock, flags);
> + hvfb_docopy(par, start, PAGE_SIZE);
> + spin_unlock_irqrestore(&par->docopy_lock, flags);
> + }
> + }
> +
> + if (par->fb_ready)
> + synthvid_update(p, 0, miny, p->var.xres, maxy + 1);
> +}
> +
> +static struct fb_deferred_io synthvid_defio = {
> + .delay = HZ / 20,
> + .deferred_io = synthvid_deferred_io,
> +};
>
> /*
> * Actions on received messages from host:
> @@ -604,7 +683,7 @@ static int synthvid_send_config(struct hv_device *hdev)
> msg->vid_hdr.type = SYNTHVID_VRAM_LOCATION;
> msg->vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
> sizeof(struct synthvid_vram_location);
> - msg->vram.user_ctx = msg->vram.vram_gpa = info->fix.smem_start;
> + msg->vram.user_ctx = msg->vram.vram_gpa = par->mmio_pp;
> msg->vram.is_vram_gpa_specified = 1;
> synthvid_send(hdev, msg);
>
> @@ -614,7 +693,7 @@ static int synthvid_send_config(struct hv_device *hdev)
> ret = -ETIMEDOUT;
> goto out;
> }
> - if (msg->vram_ack.user_ctx != info->fix.smem_start) {
> + if (msg->vram_ack.user_ctx != par->mmio_pp) {
> pr_err("Unable to set VRAM location\n");
> ret = -ENODEV;
> goto out;
> @@ -631,19 +710,82 @@ static int synthvid_send_config(struct hv_device *hdev)
>
> /*
> * Delayed work callback:
> - * It is called at HVFB_UPDATE_DELAY or longer time interval to process
> - * screen updates. It is re-scheduled if further update is necessary.
> + * It is scheduled to call whenever update request is received and it has
> + * not been called in last HVFB_ONDEMAND_THROTTLE time interval.
> */
> static void hvfb_update_work(struct work_struct *w)
> {
> struct hvfb_par *par = container_of(w, struct hvfb_par, dwork.work);
> struct fb_info *info = par->info;
> + unsigned long flags;
> + int x1, x2, y1, y2;
> + int j;
> +
> + spin_lock_irqsave(&par->delayed_refresh_lock, flags);
> + /* Reset the request flag */
> + par->delayed_refresh = false;
> +
> + /* Store the dirty rectangle to local variables */
> + x1 = par->x1;
> + x2 = par->x2;
> + y1 = par->y1;
> + y2 = par->y2;
> +
> + /* Clear dirty rectangle */
> + par->x1 = par->y1 = INT_MAX;
> + par->x2 = par->y2 = 0;
> +
> + spin_unlock_irqrestore(&par->delayed_refresh_lock, flags);
>
> + if (x1 < 0 || x1 > info->var.xres || x2 < 0 ||
> + x2 > info->var.xres || y1 < 0 || y1 > info->var.yres ||
> + y2 < 0 || y2 > info->var.yres || x2 <= x1)
> + return;
Are the tests for less than 0 needed? I think all possibility of
negative values has been eliminated.
> +
> + /* Copy the dirty rectangle to frame buffer memory */
> + spin_lock_irqsave(&par->docopy_lock, flags);
> + for (j = y1; j < y2; j++) {
> + if (j == info->var.yres)
> + break;
The above test isn't needed. The maximum value that y2 can be
is yres (that is checked a few lines above in the big "if" statement).
Since j is always less than y2, j can never be equal to yres.
> + hvfb_docopy(par,
> + j * info->fix.line_length +
> + (x1 * screen_depth / 8),
> + (x2 - x1) * screen_depth / 8);
> + }
> + spin_unlock_irqrestore(&par->docopy_lock, flags);
> +
> + /* Refresh */
> if (par->fb_ready)
> - synthvid_update(info);
> + synthvid_update(info, x1, y1, x2, y2);
> +}
> +
Michael
