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Date:   Fri, 14 Jun 2019 16:45:26 +0200
From:   Maxime Ripard <maxime.ripard@bootlin.com>
To:     Jagan Teki <jagan@amarulasolutions.com>
Cc:     David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
        Chen-Yu Tsai <wens@csie.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Bhushan Shah <bshah@mykolab.com>,
        Vasily Khoruzhick <anarsoul@gmail.com>,
        =?utf-8?B?5Z2a5a6a5YmN6KGM?= <powerpan@qq.com>,
        Michael Trimarchi <michael@amarulasolutions.com>,
        linux-amarula <linux-amarula@amarulasolutions.com>,
        linux-sunxi <linux-sunxi@googlegroups.com>
Subject: Re: [PATCH v10 01/11] drm/sun4i: dsi: Fix TCON DRQ set bits
Message-ID: <20190614144526.lorg3saj4wjopgne@flea>
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On Fri, Jun 14, 2019 at 12:03:13PM +0530, Jagan Teki wrote:
> On Thu, Jun 13, 2019 at 6:56 PM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> >
> > On Wed, Jun 05, 2019 at 01:17:11PM +0530, Jagan Teki wrote:
> > > On Tue, Jun 4, 2019 at 3:30 PM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > > >
> > > > On Wed, May 29, 2019 at 11:44:56PM +0530, Jagan Teki wrote:
> > > > > On Wed, May 29, 2019 at 8:24 PM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > > > > >
> > > > > > On Fri, May 24, 2019 at 03:48:51PM +0530, Jagan Teki wrote:
> > > > > > > On Fri, May 24, 2019 at 2:04 AM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > > > > > > >
> > > > > > > > On Mon, May 20, 2019 at 02:33:08PM +0530, Jagan Teki wrote:
> > > > > > > > > According to "DRM kernel-internal display mode structure" in
> > > > > > > > > include/drm/drm_modes.h the current driver is trying to include
> > > > > > > > > sync timings along with front porch value while checking and
> > > > > > > > > computing drq set bits in non-burst mode.
> > > > > > > > >
> > > > > > > > > mode->hsync_end - mode->hdisplay => horizontal front porch + sync
> > > > > > > > >
> > > > > > > > > With adding additional sync timings, the dsi controller leads to
> > > > > > > > > wrong drq set bits for "bananapi,s070wv20-ct16" panel which indeed
> > > > > > > > > trigger panel flip_done timed out as:
> > > > > > > > >
> > > > > > > > >  WARNING: CPU: 0 PID: 31 at drivers/gpu/drm/drm_atomic_helper.c:1429 drm_atomic_helper_wait_for_vblanks.part.1+0x298/0x2a0
> > > > > > > > >  [CRTC:46:crtc-0] vblank wait timed out
> > > > > > > > >  Modules linked in:
> > > > > > > > >  CPU: 0 PID: 31 Comm: kworker/0:1 Not tainted 5.1.0-next-20190514-00026-g01f0c75b902d-dirty #13
> > > > > > > > >  Hardware name: Allwinner sun8i Family
> > > > > > > > >  Workqueue: events deferred_probe_work_func
> > > > > > > > >  [<c010ed54>] (unwind_backtrace) from [<c010b76c>] (show_stack+0x10/0x14)
> > > > > > > > >  [<c010b76c>] (show_stack) from [<c0688c70>] (dump_stack+0x84/0x98)
> > > > > > > > >  [<c0688c70>] (dump_stack) from [<c011d9e4>] (__warn+0xfc/0x114)
> > > > > > > > >  [<c011d9e4>] (__warn) from [<c011da40>] (warn_slowpath_fmt+0x44/0x68)
> > > > > > > > >  [<c011da40>] (warn_slowpath_fmt) from [<c040cd50>] (drm_atomic_helper_wait_for_vblanks.part.1+0x298/0x2a0)
> > > > > > > > >  [<c040cd50>] (drm_atomic_helper_wait_for_vblanks.part.1) from [<c040e694>] (drm_atomic_helper_commit_tail_rpm+0x5c/0x6c)
> > > > > > > > >  [<c040e694>] (drm_atomic_helper_commit_tail_rpm) from [<c040e4dc>] (commit_tail+0x40/0x6c)
> > > > > > > > >  [<c040e4dc>] (commit_tail) from [<c040e5cc>] (drm_atomic_helper_commit+0xbc/0x128)
> > > > > > > > >  [<c040e5cc>] (drm_atomic_helper_commit) from [<c0411b64>] (restore_fbdev_mode_atomic+0x1cc/0x1dc)
> > > > > > > > >  [<c0411b64>] (restore_fbdev_mode_atomic) from [<c04156f8>] (drm_fb_helper_restore_fbdev_mode_unlocked+0x54/0xa0)
> > > > > > > > >  [<c04156f8>] (drm_fb_helper_restore_fbdev_mode_unlocked) from [<c0415774>] (drm_fb_helper_set_par+0x30/0x54)
> > > > > > > > >  [<c0415774>] (drm_fb_helper_set_par) from [<c03ad450>] (fbcon_init+0x560/0x5ac)
> > > > > > > > >  [<c03ad450>] (fbcon_init) from [<c03eb8a0>] (visual_init+0xbc/0x104)
> > > > > > > > >  [<c03eb8a0>] (visual_init) from [<c03ed1b8>] (do_bind_con_driver+0x1b0/0x390)
> > > > > > > > >  [<c03ed1b8>] (do_bind_con_driver) from [<c03ed780>] (do_take_over_console+0x13c/0x1c4)
> > > > > > > > >  [<c03ed780>] (do_take_over_console) from [<c03ad800>] (do_fbcon_takeover+0x74/0xcc)
> > > > > > > > >  [<c03ad800>] (do_fbcon_takeover) from [<c013c9c8>] (notifier_call_chain+0x44/0x84)
> > > > > > > > >  [<c013c9c8>] (notifier_call_chain) from [<c013cd20>] (__blocking_notifier_call_chain+0x48/0x60)
> > > > > > > > >  [<c013cd20>] (__blocking_notifier_call_chain) from [<c013cd50>] (blocking_notifier_call_chain+0x18/0x20)
> > > > > > > > >  [<c013cd50>] (blocking_notifier_call_chain) from [<c03a6e44>] (register_framebuffer+0x1e0/0x2f8)
> > > > > > > > >  [<c03a6e44>] (register_framebuffer) from [<c04153c0>] (__drm_fb_helper_initial_config_and_unlock+0x2fc/0x50c)
> > > > > > > > >  [<c04153c0>] (__drm_fb_helper_initial_config_and_unlock) from [<c04158c8>] (drm_fbdev_client_hotplug+0xe8/0x1b8)
> > > > > > > > >  [<c04158c8>] (drm_fbdev_client_hotplug) from [<c0415a20>] (drm_fbdev_generic_setup+0x88/0x118)
> > > > > > > > >  [<c0415a20>] (drm_fbdev_generic_setup) from [<c043f060>] (sun4i_drv_bind+0x128/0x160)
> > > > > > > > >  [<c043f060>] (sun4i_drv_bind) from [<c044b598>] (try_to_bring_up_master+0x164/0x1a0)
> > > > > > > > >  [<c044b598>] (try_to_bring_up_master) from [<c044b668>] (__component_add+0x94/0x140)
> > > > > > > > >  [<c044b668>] (__component_add) from [<c0445e1c>] (sun6i_dsi_probe+0x144/0x234)
> > > > > > > > >  [<c0445e1c>] (sun6i_dsi_probe) from [<c0452ef4>] (platform_drv_probe+0x48/0x9c)
> > > > > > > > >  [<c0452ef4>] (platform_drv_probe) from [<c04512cc>] (really_probe+0x1dc/0x2c8)
> > > > > > > > >  [<c04512cc>] (really_probe) from [<c0451518>] (driver_probe_device+0x60/0x160)
> > > > > > > > >  [<c0451518>] (driver_probe_device) from [<c044f7a4>] (bus_for_each_drv+0x74/0xb8)
> > > > > > > > >  [<c044f7a4>] (bus_for_each_drv) from [<c045107c>] (__device_attach+0xd0/0x13c)
> > > > > > > > >  [<c045107c>] (__device_attach) from [<c0450474>] (bus_probe_device+0x84/0x8c)
> > > > > > > > >  [<c0450474>] (bus_probe_device) from [<c0450900>] (deferred_probe_work_func+0x64/0x90)
> > > > > > > > >  [<c0450900>] (deferred_probe_work_func) from [<c0135970>] (process_one_work+0x204/0x420)
> > > > > > > > >  [<c0135970>] (process_one_work) from [<c013690c>] (worker_thread+0x274/0x5a0)
> > > > > > > > >  [<c013690c>] (worker_thread) from [<c013b3d8>] (kthread+0x11c/0x14c)
> > > > > > > > >  [<c013b3d8>] (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
> > > > > > > > >  Exception stack(0xde539fb0 to 0xde539ff8)
> > > > > > > > >  9fa0:                                     00000000 00000000 00000000 00000000
> > > > > > > > >  9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> > > > > > > > >  9fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> > > > > > > > >  ---[ end trace b57eb1e5c64c6b8b ]---
> > > > > > > > >  random: fast init done
> > > > > > > > >  [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [CRTC:46:crtc-0] flip_done timed out
> > > > > > > > >  [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [CONNECTOR:48:DSI-1] flip_done timed out
> > > > > > > > >  [drm:drm_atomic_helper_wait_for_dependencies] *ERROR* [PLANE:30:plane-0] flip_done timed out
> > > > > > > > >
> > > > > > > > > But according to Allwinner A33, A64 BSP code [1] [3] the TCON DRQ for
> > > > > > > > > non-burst DSI mode can be computed based on "horizontal front porch"
> > > > > > > > > value only (no sync timings included).
> > > > > > > > >
> > > > > > > > > Detailed evidence for drq set bits based on A33 BSP [1] [2]
> > > > > > > > >
> > > > > > > > > => panel->lcd_ht - panel->lcd_x - panel->lcd_hbp - 20
> > > > > > > > > => (tt->hor_front_porch + lcdp->panel_info.lcd_hbp +
> > > > > > > > > lcdp->panel_info.lcd_x) - panel->lcd_x - panel->lcd_hbp - 20
> > > > > > > > > => tt->hor_front_porch - 20
> > > > > > > >
> > > > > > > > The thing is, while your explanation on the DRM side is sound,
> > > > > > > > Allwinner has been using the hbp field of their panel description to
> > > > > > > > store what DRM calls the backporch and the sync period.
> > > > > > >
> > > > > > > Exactly, hbp = backporch + sync
> > > > > > > https://github.com/BPI-SINOVOIP/BPI-M2M-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp/de/disp_lcd.c#L2046
> > > > > > >
> > > > > > > And the above computation is rely on that as well. If you can see the
> > > > > > > final out of the above computation you can get the front porch value
> > > > > > > (w/o sync )
> > > > > >
> > > > > > As I was saying, you are explaining it well for DRM, but in order for
> > > > > > your last formula (the one coming from the BSP) to make sense, you
> > > > > > have to explain that the horizontal back porch for Allwinner contains
> > > > > > the sync period, otherwise your expansion of lcd_ht doesn't make
> > > > > > sense.
> > > > >
> > > > > I'm not sure why we need to take care of back porch since the formula
> > > > > clearly evaluating a result as front porch, without sync timing (as
> > > > > current code included this sync), I keep the hbp and trying to
> > > > > substitute the lcd_ht value so the end result would cancel hbp.
> > > >
> > > > Because it changes how lcd_ht expands. In the DRM case, it will expand
> > > > to the displayed area, the front porch, the sync period and the back
> > > > porch.
> > > >
> > > > In your case, you expand it to the displayed area, the front porch and
> > > > the back porch, precisely because in Allwinner's case, the back porch
> > > > has the sync period.
> > >
> > > I understand the point, but technically it matter about the final
> > > computation result.  May be we can even manage the same computation in
> > > back porch, but I'm not sure. Since the final output doesn't involve
> > > any sync length, why we can include that ie what I'm not sure.
> >
> > We have the following formula:
> > lcd_ht - lcd_x - lcd_hbp - 20
> >
> > Using the concepts as they are defined in DRM, this expands to:
> > x + hbp + hsync + hfp - x - hbp - 20
>
> Here is diff between allwinner hbp vs hbp in DRM.
>
> Say hbp in DRM can call it hbackporch, so
>
> => x + hbackporch + hsync + hfp - -x - hbp - 20
>
> (and here we need to substitute hbp formula from allwinner since the
> actual equation would coming from there
> https://github.com/BPI-SINOVOIP/BPI-M2M-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp/de/disp_lcd.c#L2046)

And this is precisely what needs to be said, with an explanation about
where that hor_back_porch is being used later on, and what impact it
could have.

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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