Re: [PATCH] video: hyperv_fb: Directly use the MMIO VRAM

From: Boqun Feng
Date: Sat Nov 21 2020 - 09:55:08 EST

Hi Dexuan,

On Fri, Nov 20, 2020 at 05:45:47PM -0800, Dexuan Cui wrote:
> Late in 2019, 2 commits (see the 2 Fixes tags) were introduced to
> mitigate the slow framebuffer issue. Now that we have fixed the
> slowness issue by correctly mapping the MMIO VRAM (see
> commit 5f1251a48c17 ("video: hyperv_fb: Fix the cache type when mapping
> the VRAM")), we can remove most of the code introduced by the 2 commits,
> i.e. we no longer need to allocate physical memory and use it to back up
> the VRAM in Generation-1 VM, and we also no longer need to allocate
> physical memory to back up the framebuffer in a Generation-2 VM and copy
> the framebuffer to the real VRAM.
>
> synthvid_deferred_io() is kept, because it's still desirable to send the
> SYNTHVID_DIRT message only for the exact dirty rectangle, and only when
> needed.
>
> Fixes: d21987d709e8 ("video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver")
> Fixes: 3a6fb6c4255c ("video: hyperv: hyperv_fb: Use physical memory for fb on HyperV Gen 1 VMs.")
> Cc: Wei Hu <weh@xxxxxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>

After I applied this patch and patch ("video: hyperv_fb: Fix the cache
type when mapping the VRAM") on my development branch (with Michael's
patchset for ARM64 core support on Hyper-V), and everything worked fine.
So feel free to add:

Tested-by: Boqun Feng <boqun.feng@xxxxxxxxx>

Regards,
Bqoun

> ---
>
> This patch changes drivers/video/fbdev/Kconfig, but I hope this can
> still go through the Hyper-V tree
> https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyperv-next
> because it's unlikely to cause any build issue to other fbdev drivers
> (that line was introduced by 3a6fb6c4255c only for hyperv_fb.c)
>
> Note: this patch is based on the Hyper-V tree's hyperv-fixes branch, but
> it should also apply cleanly to the branch hyperv-next if the commit
> 5f1251a48c17 is applied first. This patch is for v5.11 rather than
> v5.10.
>
> drivers/video/fbdev/Kconfig | 1 -
> drivers/video/fbdev/hyperv_fb.c | 170 ++------------------------------
> 2 files changed, 9 insertions(+), 162 deletions(-)
>
> diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
> index 402e85450bb5..05b37fb3c6d6 100644
> --- a/drivers/video/fbdev/Kconfig
> +++ b/drivers/video/fbdev/Kconfig
> @@ -2205,7 +2205,6 @@ config FB_HYPERV
> select FB_CFB_COPYAREA
> select FB_CFB_IMAGEBLIT
> select FB_DEFERRED_IO
> - select DMA_CMA if HAVE_DMA_CONTIGUOUS && CMA
> help
> This framebuffer driver supports Microsoft Hyper-V Synthetic Video.
>
> diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> index 58c74d2356ba..8131f4e66f98 100644
> --- a/drivers/video/fbdev/hyperv_fb.c
> +++ b/drivers/video/fbdev/hyperv_fb.c
> @@ -31,16 +31,6 @@
> * "set-vmvideo" command. For example
> * set-vmvideo -vmname name -horizontalresolution:1920 \
> * -verticalresolution:1200 -resolutiontype single
> - *
> - * Gen 1 VMs also support direct using VM's physical memory for framebuffer.
> - * It could improve the efficiency and performance for framebuffer and VM.
> - * This requires to allocate contiguous physical memory from Linux kernel's
> - * CMA memory allocator. To enable this, supply a kernel parameter to give
> - * enough memory space to CMA allocator for framebuffer. For example:
> - * cma=130m
> - * This gives 130MB memory to CMA allocator that can be allocated to
> - * framebuffer. For reference, 8K resolution (7680x4320) takes about
> - * 127MB memory.
> */
>
> #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> @@ -267,16 +257,8 @@ struct hvfb_par {
> /* If true, the VSC notifies the VSP on every framebuffer change */
> bool synchronous_fb;
>
> - /* If true, need to copy from deferred IO mem to framebuffer mem */
> - bool need_docopy;
> -
> struct notifier_block hvfb_panic_nb;
>
> - /* Memory for deferred IO and frame buffer itself */
> - unsigned char *dio_vp;
> - unsigned char *mmio_vp;
> - phys_addr_t mmio_pp;
> -
> /* Dirty rectangle, protected by delayed_refresh_lock */
> int x1, y1, x2, y2;
> bool delayed_refresh;
> @@ -405,21 +387,6 @@ synthvid_update(struct fb_info *info, int x1, int y1, int x2, int y2)
> return 0;
> }
>
> -static void hvfb_docopy(struct hvfb_par *par,
> - unsigned long offset,
> - unsigned long size)
> -{
> - if (!par || !par->mmio_vp || !par->dio_vp || !par->fb_ready ||
> - size == 0 || offset >= dio_fb_size)
> - return;
> -
> - if (offset + size > dio_fb_size)
> - size = dio_fb_size - offset;
> -
> - memcpy(par->mmio_vp + offset, par->dio_vp + offset, size);
> -}
> -
> -/* Deferred IO callback */
> static void synthvid_deferred_io(struct fb_info *p,
> struct list_head *pagelist)
> {
> @@ -444,10 +411,6 @@ static void synthvid_deferred_io(struct fb_info *p,
> y2 = end / p->fix.line_length;
> miny = min_t(int, miny, y1);
> maxy = max_t(int, maxy, y2);
> -
> - /* Copy from dio space to mmio address */
> - if (par->fb_ready && par->need_docopy)
> - hvfb_docopy(par, start, PAGE_SIZE);
> }
>
> if (par->fb_ready && par->update)
> @@ -704,7 +667,7 @@ 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 = par->mmio_pp;
> + msg->vram.user_ctx = msg->vram.vram_gpa = info->fix.smem_start;
> msg->vram.is_vram_gpa_specified = 1;
> synthvid_send(hdev, msg);
>
> @@ -714,7 +677,7 @@ static int synthvid_send_config(struct hv_device *hdev)
> ret = -ETIMEDOUT;
> goto out;
> }
> - if (msg->vram_ack.user_ctx != par->mmio_pp) {
> + if (msg->vram_ack.user_ctx != info->fix.smem_start) {
> pr_err("Unable to set VRAM location\n");
> ret = -ENODEV;
> goto out;
> @@ -740,7 +703,6 @@ static void hvfb_update_work(struct work_struct *w)
> 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 */
> @@ -762,14 +724,6 @@ static void hvfb_update_work(struct work_struct *w)
> y1 > info->var.yres || y2 > info->var.yres || x2 <= x1)
> return;
>
> - /* Copy the dirty rectangle to frame buffer memory */
> - if (par->need_docopy)
> - for (j = y1; j < y2; j++)
> - hvfb_docopy(par,
> - j * info->fix.line_length +
> - (x1 * screen_depth / 8),
> - (x2 - x1) * screen_depth / 8);
> -
> /* Refresh */
> if (par->fb_ready && par->update)
> synthvid_update(info, x1, y1, x2, y2);
> @@ -813,8 +767,6 @@ static int hvfb_on_panic(struct notifier_block *nb,
> par = container_of(nb, struct hvfb_par, hvfb_panic_nb);
> par->synchronous_fb = true;
> info = par->info;
> - if (par->need_docopy)
> - hvfb_docopy(par, 0, dio_fb_size);
> synthvid_update(info, 0, 0, INT_MAX, INT_MAX);
>
> return NOTIFY_DONE;
> @@ -953,62 +905,6 @@ static void hvfb_get_option(struct fb_info *info)
> return;
> }
>
> -/*
> - * Allocate enough contiguous physical memory.
> - * Return physical address if succeeded or -1 if failed.
> - */
> -static phys_addr_t hvfb_get_phymem(struct hv_device *hdev,
> - unsigned int request_size)
> -{
> - struct page *page = NULL;
> - dma_addr_t dma_handle;
> - void *vmem;
> - phys_addr_t paddr = 0;
> - unsigned int order = get_order(request_size);
> -
> - if (request_size == 0)
> - return -1;
> -
> - if (order < MAX_ORDER) {
> - /* Call alloc_pages if the size is less than 2^MAX_ORDER */
> - page = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
> - if (!page)
> - return -1;
> -
> - paddr = (page_to_pfn(page) << PAGE_SHIFT);
> - } else {
> - /* Allocate from CMA */
> - hdev->device.coherent_dma_mask = DMA_BIT_MASK(64);
> -
> - vmem = dma_alloc_coherent(&hdev->device,
> - round_up(request_size, PAGE_SIZE),
> - &dma_handle,
> - GFP_KERNEL | __GFP_NOWARN);
> -
> - if (!vmem)
> - return -1;
> -
> - paddr = virt_to_phys(vmem);
> - }
> -
> - return paddr;
> -}
> -
> -/* Release contiguous physical memory */
> -static void hvfb_release_phymem(struct hv_device *hdev,
> - phys_addr_t paddr, unsigned int size)
> -{
> - unsigned int order = get_order(size);
> -
> - if (order < MAX_ORDER)
> - __free_pages(pfn_to_page(paddr >> PAGE_SHIFT), order);
> - else
> - dma_free_coherent(&hdev->device,
> - round_up(size, PAGE_SIZE),
> - phys_to_virt(paddr),
> - paddr);
> -}
> -
>
> /* Get framebuffer memory from Hyper-V video pci space */
> static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
> @@ -1018,7 +914,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
> void __iomem *fb_virt;
> int gen2vm = efi_enabled(EFI_BOOT);
> resource_size_t pot_start, pot_end;
> - phys_addr_t paddr;
> int ret;
>
> info->apertures = alloc_apertures(1);
> @@ -1036,38 +931,12 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
>
> info->apertures->ranges[0].base = pci_resource_start(pdev, 0);
> info->apertures->ranges[0].size = pci_resource_len(pdev, 0);
> -
> - /*
> - * For Gen 1 VM, we can directly use the contiguous memory
> - * from VM. If we succeed, deferred IO happens directly
> - * on this allocated framebuffer memory, avoiding extra
> - * memory copy.
> - */
> - paddr = hvfb_get_phymem(hdev, screen_fb_size);
> - if (paddr != (phys_addr_t) -1) {
> - par->mmio_pp = paddr;
> - par->mmio_vp = par->dio_vp = __va(paddr);
> -
> - info->fix.smem_start = paddr;
> - info->fix.smem_len = screen_fb_size;
> - info->screen_base = par->mmio_vp;
> - info->screen_size = screen_fb_size;
> -
> - par->need_docopy = false;
> - goto getmem_done;
> - }
> - pr_info("Unable to allocate enough contiguous physical memory on Gen 1 VM. Using MMIO instead.\n");
> } else {
> info->apertures->ranges[0].base = screen_info.lfb_base;
> info->apertures->ranges[0].size = screen_info.lfb_size;
> }
>
> - /*
> - * Cannot use the contiguous physical memory.
> - * Allocate mmio space for framebuffer.
> - */
> - dio_fb_size =
> - screen_width * screen_height * screen_depth / 8;
> + dio_fb_size = screen_width * screen_height * screen_depth / 8;
>
> if (gen2vm) {
> pot_start = 0;
> @@ -1101,22 +970,11 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
> if (!fb_virt)
> goto err2;
>
> - /* Allocate memory for deferred IO */
> - par->dio_vp = vzalloc(round_up(dio_fb_size, PAGE_SIZE));
> - if (par->dio_vp == NULL)
> - goto err3;
> -
> - /* Physical address of FB device */
> - par->mmio_pp = par->mem->start;
> - /* Virtual address of FB device */
> - par->mmio_vp = (unsigned char *) fb_virt;
> -
> info->fix.smem_start = par->mem->start;
> info->fix.smem_len = dio_fb_size;
> - info->screen_base = par->dio_vp;
> + info->screen_base = fb_virt;
> info->screen_size = dio_fb_size;
>
> -getmem_done:
> remove_conflicting_framebuffers(info->apertures,
> KBUILD_MODNAME, false);
> if (!gen2vm)
> @@ -1125,8 +983,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
>
> return 0;
>
> -err3:
> - iounmap(fb_virt);
> err2:
> vmbus_free_mmio(par->mem->start, screen_fb_size);
> par->mem = NULL;
> @@ -1139,19 +995,12 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
> }
>
> /* Release the framebuffer */
> -static void hvfb_putmem(struct hv_device *hdev, struct fb_info *info)
> +static void hvfb_putmem(struct fb_info *info)
> {
> struct hvfb_par *par = info->par;
>
> - if (par->need_docopy) {
> - vfree(par->dio_vp);
> - iounmap(info->screen_base);
> - vmbus_free_mmio(par->mem->start, screen_fb_size);
> - } else {
> - hvfb_release_phymem(hdev, info->fix.smem_start,
> - screen_fb_size);
> - }
> -
> + iounmap(info->screen_base);
> + vmbus_free_mmio(par->mem->start, screen_fb_size);
> par->mem = NULL;
> }
>
> @@ -1170,7 +1019,6 @@ static int hvfb_probe(struct hv_device *hdev,
> par = info->par;
> par->info = info;
> par->fb_ready = false;
> - par->need_docopy = true;
> init_completion(&par->wait);
> INIT_DELAYED_WORK(&par->dwork, hvfb_update_work);
>
> @@ -1256,7 +1104,7 @@ static int hvfb_probe(struct hv_device *hdev,
>
> error:
> fb_deferred_io_cleanup(info);
> - hvfb_putmem(hdev, info);
> + hvfb_putmem(info);
> error2:
> vmbus_close(hdev->channel);
> error1:
> @@ -1286,7 +1134,7 @@ static int hvfb_remove(struct hv_device *hdev)
> vmbus_close(hdev->channel);
> hv_set_drvdata(hdev, NULL);
>
> - hvfb_putmem(hdev, info);
> + hvfb_putmem(info);
> framebuffer_release(info);
>
> return 0;
> --
> 2.19.1
>