[PATCH v6] simplefb: add clock handling code

[Grant Likely]

On Thu, Nov 13, 2014 at 7:22 PM, Hans de Goede <hdegoede at redhat.com> wrote:
> From: Luc Verhaegen <libv at skynet.be>
>
> This claims and enables clocks listed in the simple framebuffer dt node.
> This is needed so that the display engine, in case the required clocks
> are known by the kernel code and are described in the dt, will remain
> properly enabled.
>
> Signed-off-by: Luc Verhaegen <libv at skynet.be>
> [hdegoede at redhat.com: Change clks from list to dynamic array]
> Reviewed-by: Hans de Goede <hdegoede at redhat.com>
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> Acked-by: Geert Uytterhoeven <geert at linux-m68k.org>
> Reviewed-by: Maxime Ripard <maxime.ripard at free-electrons.com>
> Reviewed-by: David Herrmann <dh.herrmann at gmail.com>
> Acked-by: Grant Likely <grant.likely at linaro.org>
> --
> Changes in v4:
> -change clks from linkedlist to dynamic allocated array
> -propagate EPROBE_DEFER up from simplefb_clocks_init to simplefb_probe
> changes in v6:
> -Wrap the clock code in #ifdef CONFIG_OF, as simplefb is used on non
>  devicetree platforms too
> ---
>  drivers/video/fbdev/simplefb.c | 106 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 105 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
> index cdcf1fe..868099a 100644
> --- a/drivers/video/fbdev/simplefb.c
> +++ b/drivers/video/fbdev/simplefb.c
> @@ -26,6 +26,7 @@
>  #include <linux/module.h>
>  #include <linux/platform_data/simplefb.h>
>  #include <linux/platform_device.h>
> +#include <linux/clk-provider.h>
>
>  static struct fb_fix_screeninfo simplefb_fix = {
>         .id             = "simple",
> @@ -167,8 +168,103 @@ static int simplefb_parse_pd(struct platform_device *pdev,
>
>  struct simplefb_par {
>         u32 palette[PSEUDO_PALETTE_SIZE];
> +#ifdef CONFIG_OF
> +       int clk_count;
> +       struct clk **clks;
> +#endif
>  };
>
> +/*
> + * Clock handling code.
> + *
> + * Here we handle the clocks property of our "simple-framebuffer" dt node.
> + * This is necessary so that we can make sure that any clocks needed by
> + * the display engine that the bootloader set up for us (and for which it
> + * provided a simplefb dt node), stay up, for the life of the simplefb
> + * driver.
> + *
> + * When the driver unloads, we cleanly disable, and then release the clocks.
> + *
> + * We only complain about errors here, no action is taken as the most likely
> + * error can only happen due to a mismatch between the bootloader which set
> + * up simplefb, and the clock definitions in the device tree. Chances are
> + * that there are no adverse effects, and if there are, a clean teardown of
> + * the fb probe will not help us much either. So just complain and carry on,
> + * and hope that the user actually gets a working fb at the end of things.
> + */
> +static int
> +simplefb_clocks_init(struct simplefb_par *par, struct platform_device *pdev)

Going against convention here. Functions in the rest of the file have
the return parameters on the same line as the function name. Don't do
something different here.

Besides, it's just bad practice. Putting the return values on a
separate line means they don't show up in the results when grepping
for a function name.

> +{
> +#ifdef CONFIG_OF

Rather ugly. When #ifdefs are unavoidable, please wrap the entire
function including the prototype and have an #else block with a static
inline empty function so that the #ifdef/#endif directives don't
interfere with the indentation flow.

> +       struct device_node *np = pdev->dev.of_node;
> +       struct clk *clock;
> +       int i, ret;
> +
> +       if (dev_get_platdata(&pdev->dev) || !np)
> +               return 0;
> +
> +       par->clk_count = of_clk_get_parent_count(np);
> +       if (par->clk_count <= 0)
> +               return 0;
> +
> +       par->clks = kcalloc(par->clk_count, sizeof(struct clk *), GFP_KERNEL);
> +       if (!par->clks)
> +               return -ENOMEM;
> +
> +       for (i = 0; i < par->clk_count; i++) {
> +               clock = of_clk_get(np, i);

Should check if there is an 'of' version of devm_clk_get(). Then the
clock destroy function wouldn't be needed at all.

> +               if (IS_ERR(clock)) {
> +                       if (PTR_ERR(clock) == -EPROBE_DEFER) {
> +                               while (--i >= 0) {
> +                                       if (par->clks[i])
> +                                               clk_put(par->clks[i]);
> +                               }
> +                               kfree(par->clks);
> +                               return -EPROBE_DEFER;
> +                       }
> +                       dev_err(&pdev->dev, "%s: clock %d not found: %ld\n",
> +                               __func__, i, PTR_ERR(clock));
> +                       continue;
> +               }
> +               par->clks[i] = clock;
> +       }

(comment for a followup patch) As discussed on IRC, I don't think we
want the driver to return -EPROBE_DEFER if it can't get a clock. It
should continue anyway. The kernel knows the framebuffer is already
set up, so there is no reason to defer using it. The driver should
keep track of the clocks that it failed to obtain and try again just
before unused clocks get disabled. Have a special initcall hook that
walks though the bound framebuffers and tries the unobtained clocks
again.

> +
> +       for (i = 0; i < par->clk_count; i++) {
> +               if (par->clks[i]) {
> +                       ret = clk_prepare_enable(par->clks[i]);
> +                       if (ret) {
> +                               dev_err(&pdev->dev,
> +                                       "%s: failed to enable clock %d: %d\n",
> +                                       __func__, i, ret);
> +                               clk_put(par->clks[i]);
> +                               par->clks[i] = NULL;
> +                       }
> +               }
> +       }
> +#endif
> +       return 0;
> +}
> +
> +static void
> +simplefb_clocks_destroy(struct simplefb_par *par)
> +{
> +#ifdef CONFIG_OF
> +       int i;
> +
> +       if (!par->clks)
> +               return;
> +
> +       for (i = 0; i < par->clk_count; i++) {
> +               if (par->clks[i]) {
> +                       clk_disable_unprepare(par->clks[i]);
> +                       clk_put(par->clks[i]);
> +               }
> +       }
> +
> +       kfree(par->clks);
> +#endif
> +}
> +
>  static int simplefb_probe(struct platform_device *pdev)
>  {
>         int ret;
> @@ -236,6 +332,10 @@ static int simplefb_probe(struct platform_device *pdev)
>         }
>         info->pseudo_palette = par->palette;
>
> +       ret = simplefb_clocks_init(par, pdev);
> +       if (ret < 0)
> +               goto error_unmap;
> +
>         dev_info(&pdev->dev, "framebuffer at 0x%lx, 0x%x bytes, mapped to 0x%p\n",
>                              info->fix.smem_start, info->fix.smem_len,
>                              info->screen_base);
> @@ -247,13 +347,15 @@ static int simplefb_probe(struct platform_device *pdev)
>         ret = register_framebuffer(info);
>         if (ret < 0) {
>                 dev_err(&pdev->dev, "Unable to register simplefb: %d\n", ret);
> -               goto error_unmap;
> +               goto error_clocks;
>         }
>
>         dev_info(&pdev->dev, "fb%d: simplefb registered!\n", info->node);
>
>         return 0;
>
> +error_clocks:
> +       simplefb_clocks_destroy(par);
>  error_unmap:
>         iounmap(info->screen_base);
>  error_fb_release:
> @@ -264,8 +366,10 @@ error_fb_release:
>  static int simplefb_remove(struct platform_device *pdev)
>  {
>         struct fb_info *info = platform_get_drvdata(pdev);
> +       struct simplefb_par *par = info->par;
>
>         unregister_framebuffer(info);
> +       simplefb_clocks_destroy(par);
>         framebuffer_release(info);
>
>         return 0;
> --
> 2.1.0
>