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现成的 ADB 命令为：

dpi 计算公式： ( √(x^2 + y^2) ) / 屏幕尺寸

其实 wm 调用的就 是 上层 WindowsManger.java 的方法，最终调用到 Framework 下的 WindowsManagerServices.java 代码。

wm 执行log 如下：

px30_evb:/ # wm size 640x480 logcat 如下：10-12 08:05:46.995  1727  1727 D AndroidRuntime: Calling main entry com.android.commands.wm.Wm10-12 08:05:47.001   396   408 I WindowManager: Using new display size: 640x480

如果在驱动中写死的话，一般不建议这样修改，容易出问题：

高通平台：

--- a/kernel/msm-3.18/drivers/video/msm/mdss/mdss_fb.c+++ b/kernel/msm-3.18/drivers/video/msm/mdss/mdss_fb.c@@ -2501,8 +2501,8 @@ static int mdss_fb_register(struct msm_fb_data_type *mfd)        else                fix->line_length = var->xres * bpp; -       var->xres_virtual = var->xres;-       var->yres_virtual = panel_info->yres * mfd->fb_page;+       var->xres_virtual = 1920;	//var->xres;+       var->yres_virtual = 1080 * mfd->fb_page;        var->bits_per_pixel = bpp * 8;  /* FrameBuffer color depth */         /*@@ -3410,8 +3410,8 @@ void mdss_panelinfo_to_fb_var(struct mdss_panel_info *pinfo, {        u32 frame_rate; -       var->xres = mdss_fb_get_panel_xres(pinfo);-       var->yres = pinfo->yres;+       var->xres = 1920;		//mdss_fb_get_panel_xres(pinfo);+       var->yres = 1080;		//pinfo->yres;        var->lower_margin = pinfo->lcdc.v_front_porch -                pinfo->prg_fet;        var->upper_margin = pinfo->lcdc.v_back_porch +

rockchip 平台

参考：

@ kernel\drivers\video\fbdev\core\modedb.c/** * fb_videomode_to_var - convert fb_videomode to fb_var_screeninfo * @var: pointer to struct fb_var_screeninfo * @mode: pointer to struct fb_videomode */void fb_videomode_to_var(struct fb_var_screeninfo *var,			 const struct fb_videomode *mode){
   	var->xres = mode->xres;	var->yres = mode->yres;	var->xres_virtual = mode->xres;	var->yres_virtual = mode->yres;	var->xoffset = 0;	var->yoffset = 0;	var->pixclock = mode->pixclock;	var->left_margin = mode->left_margin;	var->right_margin = mode->right_margin;	var->upper_margin = mode->upper_margin;	var->lower_margin = mode->lower_margin;	var->hsync_len = mode->hsync_len;	var->vsync_len = mode->vsync_len;	var->sync = mode->sync;	var->vmode = mode->vmode & FB_VMODE_MASK;}

@ kernel\drivers\video\rockchip\rk_fb.cint rk_fb_register(struct rk_lcdc_driver *dev_drv,		   struct rk_lcdc_win *win, int id){
   	struct rk_fb *rk_fb = platform_get_drvdata(fb_pdev);	struct fb_info *fbi;	struct rk_fb_par *fb_par = NULL;	int i = 0, ret = 0, index = 0;	unsigned long flags;	char time_line_name[16];	int mirror = 0;	if (rk_fb->num_lcdc == RK30_MAX_LCDC_SUPPORT)		return -ENXIO;	for (i = 0; i < RK30_MAX_LCDC_SUPPORT; i++) {
   		if (!rk_fb->lcdc_dev_drv[i]) {
   			rk_fb->lcdc_dev_drv[i] = dev_drv;			rk_fb->lcdc_dev_drv[i]->id = id;			rk_fb->num_lcdc++;			break;		}	}	index = i;	init_lcdc_device_driver(rk_fb, win, index);	dev_drv->fb_index_base = rk_fb->num_fb;	for (i = 0; i < dev_drv->lcdc_win_num; i++) {
   		fbi = framebuffer_alloc(0, &fb_pdev->dev);		if (!fbi) {
   			dev_err(&fb_pdev->dev, "fb framebuffer_alloc fail!");			return -ENOMEM;		}		fb_par = devm_kzalloc(&fb_pdev->dev, sizeof(struct rk_fb_par),				      GFP_KERNEL);		if (!fb_par) {
   			dev_err(&fb_pdev->dev, "malloc fb_par for fb%d fail!",				rk_fb->num_fb);			return -ENOMEM;		}		fb_par->id = rk_fb->num_fb;		fb_par->lcdc_drv = dev_drv;		fbi->par = (void *)fb_par;		fbi->var = def_var;		fbi->fix = def_fix;		sprintf(fbi->fix.id, "fb%d", rk_fb->num_fb);		fb_videomode_to_var(&fbi->var, &dev_drv->cur_screen->mode);		if (dev_drv->dsp_mode == ONE_VOP_DUAL_MIPI_VER_SCAN) {
   			fbi->var.xres /= 2;			fbi->var.yres *= 2;			fbi->var.xres_virtual /= 2;			fbi->var.yres_virtual *= 2;		}		fbi->var.width = dev_drv->cur_screen->width;		fbi->var.height = dev_drv->cur_screen->height;		fbi->var.grayscale |=		    ((fbi->var.xres & 0xfff) << 8) + (fbi->var.yres << 20);		fbi->var.reserved[0] |= (fbi->var.xres >> 12);#if defined(CONFIG_LOGO_LINUX_BMP)		fbi->var.bits_per_pixel = 32;#else		fbi->var.bits_per_pixel = 16;#endif		fbi->fix.line_length =		    (fbi->var.xres_virtual) * (fbi->var.bits_per_pixel >> 3);		if (dev_drv->iommu_enabled)			fb_ops.fb_mmap = rk_fb_mmap;		fbi->fbops = &fb_ops;		fbi->flags = FBINFO_FLAG_DEFAULT;		fbi->pseudo_palette = dev_drv->win[i]->pseudo_pal;		ret = register_framebuffer(fbi);		if (ret < 0) {
   			dev_err(&fb_pdev->dev,				"%s fb%d register_framebuffer fail!\n",				__func__, rk_fb->num_fb);			return ret;		}		rkfb_create_sysfs(fbi);		rk_fb->fb[rk_fb->num_fb] = fbi;		dev_info(fbi->dev, "rockchip framebuffer registerd:%s\n",			 fbi->fix.id);		rk_fb->num_fb++;		if (i == 0) {
   			init_waitqueue_head(&dev_drv->vsync_info.wait);			init_waitqueue_head(&dev_drv->update_regs_wait);			ret = device_create_file(fbi->dev, &dev_attr_vsync);			if (ret)				dev_err(fbi->dev,					"failed to create vsync file\n");			dev_drv->vsync_info.thread =			    kthread_run(rk_fb_wait_for_vsync_thread, dev_drv,					"fb-vsync");			if (dev_drv->vsync_info.thread == ERR_PTR(-ENOMEM)) {
   				dev_err(fbi->dev,					"failed to run vsync thread\n");				dev_drv->vsync_info.thread = NULL;			}			dev_drv->vsync_info.active = 1;			mutex_init(&dev_drv->output_lock);			INIT_LIST_HEAD(&dev_drv->update_regs_list);			INIT_LIST_HEAD(&dev_drv->saved_list);			mutex_init(&dev_drv->update_regs_list_lock);			init_kthread_worker(&dev_drv->update_regs_worker);			dev_drv->update_regs_thread =			    kthread_run(kthread_worker_fn,					&dev_drv->update_regs_worker, "rk-fb");			if (IS_ERR(dev_drv->update_regs_thread)) {
   				int err = PTR_ERR(dev_drv->update_regs_thread);				dev_drv->update_regs_thread = NULL;				pr_info("failed to run update_regs thread\n");				return err;			}			init_kthread_work(&dev_drv->update_regs_work,					  rk_fb_update_regs_handler);			snprintf(time_line_name, sizeof(time_line_name),				 "vop%d-timeline", id);			dev_drv->timeline =			    sw_sync_timeline_create(time_line_name);			dev_drv->timeline_max = 1;		}	}	/* show logo for primary display device */#if !defined(CONFIG_FRAMEBUFFER_CONSOLE)	if (dev_drv->prop == PRMRY) {
   		u16 xact, yact;		int format;		u32 dsp_addr;		struct fb_info *main_fbi = rk_fb->fb[0];		main_fbi->fbops->fb_open(main_fbi, 1);		main_fbi->var.pixclock = dev_drv->pixclock;		if (dev_drv->iommu_enabled) {
   			if (dev_drv->mmu_dev)				rockchip_iovmm_set_fault_handler(dev_drv->dev,						rk_fb_sysmmu_fault_handler);		}		rk_fb_alloc_buffer(main_fbi);	/* only alloc memory for main fb */		dev_drv->uboot_logo = support_uboot_display();		if (dev_drv->uboot_logo &&		    uboot_logo_offset && uboot_logo_base) {
   			int width, height, bits, xvir;			phys_addr_t start = uboot_logo_base + uboot_logo_offset;			unsigned int size = uboot_logo_size - uboot_logo_offset;			unsigned int nr_pages;			int ymirror = 0;			struct page **pages;			char *vaddr;			int logo_len, i = 0;			if (dev_drv->ops->get_dspbuf_info)				dev_drv->ops->get_dspbuf_info(dev_drv, &xact,					&yact, &format,	&dsp_addr, &ymirror);			logo_len = rk_fb_pixel_width(format) * xact * yact >> 3;			nr_pages = size >> PAGE_SHIFT;			pages = kzalloc(sizeof(struct page) * nr_pages,					GFP_KERNEL);			if (!pages)				return -ENOMEM;			while (i < nr_pages) {
   				pages[i] = phys_to_page(start);				start += PAGE_SIZE;				i++;			}			vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);			if (!vaddr) {
   				pr_err("failed to vmap phy addr 0x%lx\n",				       (long)(uboot_logo_base +				       uboot_logo_offset));				kfree(pages);				return -1;			}			if (bmpdecoder(vaddr, main_fbi->screen_base, &width,				       &height, &bits)) {
   				kfree(pages);				vunmap(vaddr);				return 0;			}			kfree(pages);			vunmap(vaddr);			if (width != xact || height != yact) {
   				pr_err("can't support uboot kernel logo use different size [%dx%d] != [%dx%d]\n",				       xact, yact, width, height);				return 0;			}			xvir = ALIGN(width * bits, 1 << 5) >> 5;			ymirror = 0;			local_irq_save(flags);			if (dev_drv->ops->wait_frame_start)				dev_drv->ops->wait_frame_start(dev_drv, 0);			mirror = ymirror || dev_drv->cur_screen->y_mirror;			if (dev_drv->ops->post_dspbuf) {
   				dev_drv->ops->post_dspbuf(dev_drv,					main_fbi->fix.smem_start +					(mirror ? logo_len : 0),					rk_fb_data_fmt(0, bits),					width, height, xvir,					ymirror);			}			if (dev_drv->iommu_enabled) {
   				rk_fb_poll_wait_frame_complete();				if (dev_drv->ops->mmu_en)					dev_drv->ops->mmu_en(dev_drv);				freed_index = 0;			}			local_irq_restore(flags);			return 0;		} else if (dev_drv->uboot_logo && uboot_logo_base) {
   			u32 start = uboot_logo_base;			int logo_len, i = 0;			int y_mirror = 0;			unsigned int nr_pages;			struct page **pages;			char *vaddr;			int align = 0, xvir;			dev_drv->ops->get_dspbuf_info(dev_drv, &xact,						      &yact, &format,						      &start,						      &y_mirror);			logo_len = rk_fb_pixel_width(format) * xact * yact >> 3;			if (logo_len > uboot_logo_size ||			    logo_len > main_fbi->fix.smem_len) {
   				pr_err("logo size > uboot reserve buffer size\n");				return -1;			}			if (y_mirror)				start -= logo_len;			align = start % PAGE_SIZE;			start -= align;			nr_pages = PAGE_ALIGN(logo_len + align) >> PAGE_SHIFT;			pages = kzalloc(sizeof(struct page) * nr_pages,					GFP_KERNEL);			if (!pages)				return -ENOMEM;			while (i < nr_pages) {
   				pages[i] = phys_to_page(start);				start += PAGE_SIZE;				i++;			}			vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);			if (!vaddr) {
   				pr_err("failed to vmap phy addr 0x%x\n",				       start);				kfree(pages);				return -1;			}			memcpy(main_fbi->screen_base, vaddr + align, logo_len);			kfree(pages);			vunmap(vaddr);			xvir = ALIGN(xact * rk_fb_pixel_width(format),				     1 << 5) >> 5;			local_irq_save(flags);			if (dev_drv->ops->wait_frame_start)				dev_drv->ops->wait_frame_start(dev_drv, 0);			mirror = y_mirror || dev_drv->cur_screen->y_mirror;			dev_drv->ops->post_dspbuf(dev_drv,					main_fbi->fix.smem_start +					(mirror ? logo_len : 0),					format,	xact, yact,					xvir,					y_mirror);			if (dev_drv->iommu_enabled) {
   				rk_fb_poll_wait_frame_complete();				if (dev_drv->ops->mmu_en)					dev_drv->ops->mmu_en(dev_drv);				freed_index = 0;			}			local_irq_restore(flags);			return 0;		} else {
   			if (dev_drv->iommu_enabled) {
   				if (dev_drv->ops->mmu_en)					dev_drv->ops->mmu_en(dev_drv);				freed_index = 0;			}		}#if defined(CONFIG_LOGO)		main_fbi->fbops->fb_set_par(main_fbi);#if  defined(CONFIG_LOGO_LINUX_BMP)		if (fb_prewine_bmp_logo(main_fbi, FB_ROTATE_UR)) {
   			fb_set_cmap(&main_fbi->cmap, main_fbi);			fb_show_bmp_logo(main_fbi, FB_ROTATE_UR);		}#else		if (fb_prepare_logo(main_fbi, FB_ROTATE_UR)) {
   			fb_set_cmap(&main_fbi->cmap, main_fbi);			fb_show_logo(main_fbi, FB_ROTATE_UR);		}#endif		main_fbi->fbops->fb_pan_display(&main_fbi->var, main_fbi);#endif	} else {
   		struct fb_info *extend_fbi = rk_fb->fb[dev_drv->fb_index_base];		extend_fbi->var.pixclock = rk_fb->fb[0]->var.pixclock;		if (rk_fb->disp_mode == DUAL_LCD) {
   			extend_fbi->fbops->fb_open(extend_fbi, 1);			if (dev_drv->iommu_enabled) {
   				if (dev_drv->mmu_dev)					rockchip_iovmm_set_fault_handler(dev_drv->dev,									 rk_fb_sysmmu_fault_handler);			}			rk_fb_alloc_buffer(extend_fbi);		}	}#endif	return 0;}

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