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SubjectRe: [PATCH v3 3/3] console/fbcon: Add support for deferred console takeover
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Hi,

On 28-06-18 10:37, Daniel Vetter wrote:
> On Thu, Jun 28, 2018 at 10:20 AM, Hans de Goede <hdegoede@redhat.com> wrote:
>> Hi,
>>
>> On 28-06-18 09:55, Daniel Vetter wrote:
>>>
>>> On Tue, Jun 26, 2018 at 08:36:12PM +0200, Hans de Goede wrote:
>>>>
>>>> Currently fbcon claims fbdevs as soon as they are registered and takes
>>>> over
>>>> the console as soon as the first fbdev gets registered.
>>>>
>>>> This behavior is undesirable in cases where a smooth graphical bootup is
>>>> desired, in such cases we typically want the contents of the framebuffer
>>>> (typically a vendor logo) to stay in place as is.
>>>>
>>>> The current solution for this problem (on embedded systems) is to not
>>>> enable fbcon.
>>>>
>>>> This commit adds a new FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER config
>>>> option,
>>>> which when enabled defers fbcon taking over the console from the dummy
>>>> console until the first text is displayed on the console. Together with
>>>> the
>>>> "quiet" kernel commandline option, this allows fbcon to still be used
>>>> together with a smooth graphical bootup, having it take over the console
>>>> as
>>>> soon as e.g. an error message is logged.
>>>>
>>>> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>>>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>>>
>>>
>>> A bit a late comment, and feel free to reject: Have you considered
>>> registering the fbcon driver, but not doing any modesets until the very
>>> first real message shows up?
>>
>>
>> I have tried something like that, but it did not work out, this patch-set
>> actually is my 3th attempt at this (the other 2 were never posted
>> because they did not work).
>>
>> The fbcon code is woven quite tightly into the console code, so this was
>> the only clean way I could find to achieve what I want.
>
> I assumed/feared as much. Would be good to cover that in the commit
> message, to justify your approach better.

Ok, v5 with an updated commit message (and without any code changes)
coming up.

Regards,

Hans



>>>> ---
>>>> Changes in v2:
>>>> -Check the whole string when checking for erases in putcs, instead of
>>>> just
>>>> the first char
>>>> -Make dummycon_blank return 1, so that a redraw gets triggered and any
>>>> text
>>>> rendered while blanked gets output so that it can trigger a deferred
>>>> takeover if one is pending
>>>>
>>>> Changes in v3:
>>>> -Call WARN_CONSOLE_UNLOCKED() from fbcon_output_notifier()
>>>> -Unregister the notifier on fbcon_exit()
>>>> -Document the fbcon=nodefer commandline option in
>>>> Documentation/fb/fbcon.txt
>>>> ---
>>>> Documentation/fb/fbcon.txt | 7 ++++
>>>> drivers/video/console/Kconfig | 11 +++++
>>>> drivers/video/console/dummycon.c | 67 +++++++++++++++++++++++++----
>>>> drivers/video/fbdev/core/fbcon.c | 72 ++++++++++++++++++++++++++++++++
>>>> include/linux/console.h | 5 +++
>>>> 5 files changed, 154 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/Documentation/fb/fbcon.txt b/Documentation/fb/fbcon.txt
>>>> index 79c22d096bbc..d4d642e1ce9c 100644
>>>> --- a/Documentation/fb/fbcon.txt
>>>> +++ b/Documentation/fb/fbcon.txt
>>>> @@ -155,6 +155,13 @@ C. Boot options
>>>> used by text. By default, this area will be black. The 'color'
>>>> value
>>>> is an integer number that depends on the framebuffer driver being
>>>> used.
>>>> +6. fbcon=nodefer
>>>> +
>>>> + If the kernel is compiled with deferred fbcon takeover support,
>>>> normally
>>>> + the framebuffer contents, left in place by the
>>>> firmware/bootloader, will
>>>> + be preserved until there actually is some text is output to the
>>>> console.
>>>> + This option causes fbcon to bind immediately to the fbdev device.
>>>> +
>>>> C. Attaching, Detaching and Unloading
>>>> Before going on how to attach, detach and unload the framebuffer
>>>> console, an
>>>> diff --git a/drivers/video/console/Kconfig
>>>> b/drivers/video/console/Kconfig
>>>> index 4110ba7d7ca9..e91edef98633 100644
>>>> --- a/drivers/video/console/Kconfig
>>>> +++ b/drivers/video/console/Kconfig
>>>> @@ -150,6 +150,17 @@ config FRAMEBUFFER_CONSOLE_ROTATION
>>>> such that other users of the framebuffer will remain normally
>>>> oriented.
>>>> +config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
>>>> + bool "Framebuffer Console Deferred Takeover"
>>>> + depends on FRAMEBUFFER_CONSOLE=y && DUMMY_CONSOLE=y
>>>> + help
>>>> + If enabled this defers the framebuffer console taking over the
>>>> + console from the dummy console until the first text is
>>>> displayed on
>>>> + the console. This is useful in combination with the "quiet"
>>>> kernel
>>>> + commandline option to keep the framebuffer contents initially
>>>> put up
>>>> + by the firmware in place, rather then replacing the contents
>>>> with a
>>>> + black screen as soon as fbcon loads.
>>>> +
>>>> config STI_CONSOLE
>>>> bool "STI text console"
>>>> depends on PARISC && HAS_IOMEM
>>>> diff --git a/drivers/video/console/dummycon.c
>>>> b/drivers/video/console/dummycon.c
>>>> index f2eafe2ed980..45ad925ad5f8 100644
>>>> --- a/drivers/video/console/dummycon.c
>>>> +++ b/drivers/video/console/dummycon.c
>>>> @@ -26,6 +26,65 @@
>>>> #define DUMMY_ROWS CONFIG_DUMMY_CONSOLE_ROWS
>>>> #endif
>>>> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
>>>> +/* These are both protected by the console_lock */
>>>> +static RAW_NOTIFIER_HEAD(dummycon_output_nh);
>>>> +static bool dummycon_putc_called;
>>>> +
>>>> +void dummycon_register_output_notifier(struct notifier_block *nb)
>>>> +{
>>>> + raw_notifier_chain_register(&dummycon_output_nh, nb);
>>>> +
>>>> + if (dummycon_putc_called)
>>>> + nb->notifier_call(nb, 0, NULL);
>>>> +}
>>>> +
>>>> +void dummycon_unregister_output_notifier(struct notifier_block *nb)
>>>> +{
>>>> + raw_notifier_chain_unregister(&dummycon_output_nh, nb);
>>>> +}
>>>> +
>>>> +static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos)
>>>> +{
>>>> + dummycon_putc_called = true;
>>>> + raw_notifier_call_chain(&dummycon_output_nh, 0, NULL);
>>>> +}
>>>> +
>>>> +static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
>>>> + int count, int ypos, int xpos)
>>>> +{
>>>> + int i;
>>>> +
>>>> + if (!dummycon_putc_called) {
>>>> + /* Ignore erases */
>>>> + for (i = 0 ; i < count; i++) {
>>>> + if (s[i] != vc->vc_video_erase_char)
>>>> + break;
>>>> + }
>>>> + if (i == count)
>>>> + return;
>>>> +
>>>> + dummycon_putc_called = true;
>>>> + }
>>>> +
>>>> + raw_notifier_call_chain(&dummycon_output_nh, 0, NULL);
>>>> +}
>>>> +
>>>> +static int dummycon_blank(struct vc_data *vc, int blank, int
>>>> mode_switch)
>>>> +{
>>>> + /* Redraw, so that we get putc(s) for output done while blanked
>>>> */
>>>> + return 1;
>>>> +}
>>>> +#else
>>>> +static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos)
>>>> { }
>>>> +static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
>>>> + int count, int ypos, int xpos) { }
>>>> +static int dummycon_blank(struct vc_data *vc, int blank, int
>>>> mode_switch)
>>>> +{
>>>> + return 0;
>>>> +}
>>>> +#endif
>>>> +
>>>> static const char *dummycon_startup(void)
>>>> {
>>>> return "dummy device";
>>>> @@ -44,9 +103,6 @@ static void dummycon_init(struct vc_data *vc, int
>>>> init)
>>>> static void dummycon_deinit(struct vc_data *vc) { }
>>>> static void dummycon_clear(struct vc_data *vc, int sy, int sx, int
>>>> height,
>>>> int width) { }
>>>> -static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos)
>>>> { }
>>>> -static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
>>>> - int count, int ypos, int xpos) { }
>>>> static void dummycon_cursor(struct vc_data *vc, int mode) { }
>>>> static bool dummycon_scroll(struct vc_data *vc, unsigned int top,
>>>> @@ -61,11 +117,6 @@ static int dummycon_switch(struct vc_data *vc)
>>>> return 0;
>>>> }
>>>> -static int dummycon_blank(struct vc_data *vc, int blank, int
>>>> mode_switch)
>>>> -{
>>>> - return 0;
>>>> -}
>>>> -
>>>> static int dummycon_font_set(struct vc_data *vc, struct console_font
>>>> *font,
>>>> unsigned int flags)
>>>> {
>>>> diff --git a/drivers/video/fbdev/core/fbcon.c
>>>> b/drivers/video/fbdev/core/fbcon.c
>>>> index cd8d52a967aa..5fb156bdcf4e 100644
>>>> --- a/drivers/video/fbdev/core/fbcon.c
>>>> +++ b/drivers/video/fbdev/core/fbcon.c
>>>> @@ -129,6 +129,12 @@ static inline void fbcon_map_override(void)
>>>> }
>>>> #endif /* CONFIG_FRAMEBUFFER_CONSOLE_DETECT_PRIMARY */
>>>> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
>>>> +static bool deferred_takeover = true;
>>>> +#else
>>>> +#define deferred_takeover false
>>>> +#endif
>>>> +
>>>> /* font data */
>>>> static char fontname[40];
>>>> @@ -499,6 +505,12 @@ static int __init fb_console_setup(char *this_opt)
>>>> margin_color = simple_strtoul(options,
>>>> &options, 0);
>>>> continue;
>>>> }
>>>> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
>>>> + if (!strcmp(options, "nodefer")) {
>>>> + deferred_takeover = false;
>>>> + continue;
>>>> + }
>>>> +#endif
>>>> }
>>>> return 1;
>>>> }
>>>> @@ -3100,6 +3112,9 @@ static int fbcon_fb_unregistered(struct fb_info
>>>> *info)
>>>> WARN_CONSOLE_UNLOCKED();
>>>> + if (deferred_takeover)
>>>> + return 0;
>>>> +
>>>> idx = info->node;
>>>> for (i = first_fb_vc; i <= last_fb_vc; i++) {
>>>> if (con2fb_map[i] == idx)
>>>> @@ -3140,6 +3155,13 @@ static void fbcon_remap_all(int idx)
>>>> WARN_CONSOLE_UNLOCKED();
>>>> + if (deferred_takeover) {
>>>> + for (i = first_fb_vc; i <= last_fb_vc; i++)
>>>> + con2fb_map_boot[i] = idx;
>>>> + fbcon_map_override();
>>>> + return;
>>>> + }
>>>> +
>>>> for (i = first_fb_vc; i <= last_fb_vc; i++)
>>>> set_con2fb_map(i, idx, 0);
>>>> @@ -3191,6 +3213,11 @@ static int fbcon_fb_registered(struct fb_info
>>>> *info)
>>>> idx = info->node;
>>>> fbcon_select_primary(info);
>>>> + if (deferred_takeover) {
>>>> + pr_info("fbcon: Deferring console take-over\n");
>>>> + return 0;
>>>> + }
>>>> +
>>>> if (info_idx == -1) {
>>>> for (i = first_fb_vc; i <= last_fb_vc; i++) {
>>>> if (con2fb_map_boot[i] == idx) {
>>>> @@ -3566,8 +3593,46 @@ static int fbcon_init_device(void)
>>>> return 0;
>>>> }
>>>> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
>>>> +static struct notifier_block fbcon_output_nb;
>>>> +
>>>> +static int fbcon_output_notifier(struct notifier_block *nb,
>>>> + unsigned long action, void *data)
>>>> +{
>>>> + int i;
>>>> +
>>>> + WARN_CONSOLE_UNLOCKED();
>>>> +
>>>> + pr_info("fbcon: Taking over console\n");
>>>> +
>>>> + dummycon_unregister_output_notifier(&fbcon_output_nb);
>>>> + deferred_takeover = false;
>>>> + logo_shown = FBCON_LOGO_DONTSHOW;
>>>> +
>>>> + for (i = 0; i < FB_MAX; i++) {
>>>> + if (registered_fb[i])
>>>> + fbcon_fb_registered(registered_fb[i]);
>>>> + }
>>>> +
>>>> + return NOTIFY_OK;
>>>> +}
>>>> +
>>>> +static void fbcon_register_output_notifier(void)
>>>> +{
>>>> + fbcon_output_nb.notifier_call = fbcon_output_notifier;
>>>> + dummycon_register_output_notifier(&fbcon_output_nb);
>>>> +}
>>>> +#else
>>>> +static inline void fbcon_register_output_notifier(void) {}
>>>> +#endif
>>>> +
>>>> static void fbcon_start(void)
>>>> {
>>>> + if (deferred_takeover) {
>>>> + fbcon_register_output_notifier();
>>>> + return;
>>>> + }
>>>> +
>>>> if (num_registered_fb) {
>>>> int i;
>>>> @@ -3594,6 +3659,13 @@ static void fbcon_exit(void)
>>>> if (fbcon_has_exited)
>>>> return;
>>>> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
>>>> + if (deferred_takeover) {
>>>> + dummycon_unregister_output_notifier(&fbcon_output_nb);
>>>> + deferred_takeover = false;
>>>> + }
>>>> +#endif
>>>> +
>>>> kfree((void *)softback_buf);
>>>> softback_buf = 0UL;
>>>> diff --git a/include/linux/console.h b/include/linux/console.h
>>>> index dfd6b0e97855..f59f3dbca65c 100644
>>>> --- a/include/linux/console.h
>>>> +++ b/include/linux/console.h
>>>> @@ -21,6 +21,7 @@ struct console_font_op;
>>>> struct console_font;
>>>> struct module;
>>>> struct tty_struct;
>>>> +struct notifier_block;
>>>> /*
>>>> * this is what the terminal answers to a ESC-Z or csi0c query.
>>>> @@ -220,4 +221,8 @@ static inline bool vgacon_text_force(void) { return
>>>> false; }
>>>> extern void console_init(void);
>>>> +/* For deferred console takeover */
>>>> +void dummycon_register_output_notifier(struct notifier_block *nb);
>>>> +void dummycon_unregister_output_notifier(struct notifier_block *nb);
>>>> +
>>>> #endif /* _LINUX_CONSOLE_H */
>>>> --
>>>> 2.17.1
>>>>
>>>> _______________________________________________
>>>> dri-devel mailing list
>>>> dri-devel@lists.freedesktop.org
>>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>>>
>>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
>
>

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