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Date: Mon, 13 Aug 2012 10:04:14 +1000
From: Ryan Mallon <rmallon@...il.com>
To: David Herrmann <dh.herrmann@...glemail.com>
CC: linux-fbdev@...r.kernel.org,
Florian Tobias Schandinat <FlorianSchandinat@....de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-serial@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
linux-kernel@...r.kernel.org,
Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH 07/11] fblog: allow selecting fbs via sysfs and module-parameters
On 13/08/12 00:53, David Herrmann wrote:
> fblog is mainly useful during boot, reboot, panics and maintenance. In all
> cases you often want to control which monitors are used for console
> output. Moreover, in multi-seat environments it is desireable to reduce
> system-overhead by not drawing the console to all framebuffers. Four
> mechanisms to select framebuffers for fblog are added:
>
> 1) "active" module parameter: This parameter selects whether fblog has
> access to available framebuffer devices. If it is true, then fblog will
> open devices following the rules described below and rendering will take
> place. If it is false, new hotplugged devices will not be activated and no
> more rendering to currently active devices takes place. However, active
> devices will continue rendering after this is set to true again.
>
> 2) "active" sysfs attribute for each fblog object. Reading this value
> returns whether a framebuffer is currently active. Writing it opens/closes
> the framebuffer. This allows runtime control which fbs are used. For
> instance, init can set these to 0 after bootup.
> Note that a framebuffer is only active if this is 1 _and_ the "active"
> module parameter is set to "true".
>
> 3) "activate_on_hotplug" module parameter: This selects whether a device
> is activated by default when hotplugged. This is true by default so new
> devices will be automatically activated.
>
> 4) "main_only" module parameter: This selects what devices are activated
> on hotplug. This has no effect if "activate_on_hotplug" is false.
> Otherwise, if this is true then only fb0 will be activated on hotplug.
> This is false by default.
>
> Signed-off-by: David Herrmann <dh.herrmann@...glemail.com>
> ---
> drivers/video/console/fblog.c | 66 ++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 65 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/video/console/fblog.c b/drivers/video/console/fblog.c
> index 1c526c5..aed77dc 100644
> --- a/drivers/video/console/fblog.c
> +++ b/drivers/video/console/fblog.c
> @@ -44,6 +44,9 @@ struct fblog_fb {
>
> static DEFINE_MUTEX(fblog_registration_lock);
> static struct fblog_fb *fblog_fbs[FB_MAX];
> +static bool active = true;
> +static bool activate_on_hotplug = true;
> +static bool main_only = false;
>
> #define to_fblog_dev(_d) container_of(_d, struct fblog_fb, dev)
>
> @@ -63,6 +66,9 @@ static int fblog_open(struct fblog_fb *fb)
> {
> int ret;
>
> + if (!active)
> + return -EPERM;
> +
> mutex_lock(&fb->lock);
>
> if (test_bit(FBLOG_KILLED, &fb->flags)) {
> @@ -115,6 +121,40 @@ static void fblog_close(struct fblog_fb *fb, bool kill_dev)
> mutex_unlock(&fb->lock);
> }
>
> +static ssize_t fblog_dev_active_show(struct device *dev,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + struct fblog_fb *fb = to_fblog_dev(dev);
> +
> + return snprintf(buf, PAGE_SIZE, "%d\n",
> + !!test_bit(FBLOG_OPEN, &fb->flags));
Nitpick. sprintf is okay here, %d is rarely longer than PAGE_SIZE :-).
> +}
> +
> +static ssize_t fblog_dev_active_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf,
> + size_t count)
> +{
> + struct fblog_fb *fb = to_fblog_dev(dev);
> + unsigned long num;
> + int ret = 0;
> +
> + num = simple_strtoul(buf, NULL, 10);
kstrtoul is preferred these days I think, it also catches errors.
> +
> + mutex_lock(&fb->info->lock);
> + if (num)
> + ret = fblog_open(fb);
> + else
> + fblog_close(fb, false);
> + mutex_unlock(&fb->info->lock);
> +
> + return ret ? ret : count;
Nitpick, you can use gcc's shortcut form of the ? operator here:
return ret ?: count;
> +}
> +
> +static DEVICE_ATTR(active, S_IRUGO | S_IWUSR | S_IWGRP, fblog_dev_active_show,
> + fblog_dev_active_store);
> +
> /*
> * fblog framebuffer list
> * The fblog_fbs[] array contains all currently registered framebuffers. If a
> @@ -148,6 +188,7 @@ static void fblog_do_unregister(struct fb_info *info)
> fblog_fbs[info->node] = NULL;
>
> fblog_close(fb, true);
> + device_remove_file(&fb->dev, &dev_attr_active);
> device_del(&fb->dev);
> put_device(&fb->dev);
> }
> @@ -156,6 +197,7 @@ static void fblog_do_register(struct fb_info *info, bool force)
> {
> struct fblog_fb *fb;
> int ret;
> + bool do_open = true;
>
> fb = fblog_fbs[info->node];
> if (fb && fb->info != info) {
> @@ -186,7 +228,20 @@ static void fblog_do_register(struct fb_info *info, bool force)
> return;
> }
>
> - fblog_open(fb);
> + ret = device_create_file(&fb->dev, &dev_attr_active);
> + if (ret) {
> + pr_err("fblog: cannot create sysfs entry");
Shouldn't need the "fblog: " prefix, since you have pr_fmt defined.
> + /* do not open fb if we cannot create control file */
> + do_open = false;
> + }
> +
> + if (!activate_on_hotplug)
> + do_open = false;
> + if (main_only && info->node != 0)
> + do_open = false;
> +
> + if (do_open)
> + fblog_open(fb);
> }
>
> static void fblog_register(struct fb_info *info, bool force)
> @@ -321,6 +376,15 @@ static void __exit fblog_exit(void)
> }
> }
>
> +module_param(active, bool, S_IRUGO | S_IWUSR | S_IWGRP);
> +MODULE_PARM_DESC(active, "Activate fblog rendering");
> +
> +module_param(activate_on_hotplug, bool, S_IRUGO | S_IWUSR | S_IWGRP);
> +MODULE_PARM_DESC(activate_on_hotplug, "Activate fblog on hotplugged devices");
> +
> +module_param(main_only, bool, S_IRUGO);
> +MODULE_PARM_DESC(main_only, "Activate fblog by default only on main devices");
> +
> module_init(fblog_init);
> module_exit(fblog_exit);
> MODULE_LICENSE("GPL");
>
--
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