linux-kernel - Re: [PATCHv3] drivers/amba: add reset control to amba bus probe

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Message-ID: <CAL_JsqLJN3n6A3NWX=pEYSPfnvQFsdBYwqr9iREHWGFwL2wHYQ@mail.gmail.com>
Date:   Tue, 13 Aug 2019 15:49:58 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Dinh Nguyen <dinguyen@...nel.org>,
        Russell King <linux@...linux.org.uk>
Cc:     devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCHv3] drivers/amba: add reset control to amba bus probe

+Russell

On Thu, Aug 8, 2019 at 8:02 AM Dinh Nguyen <dinguyen@...nel.org> wrote:
>
> The primecell controller on some SoCs, i.e. SoCFPGA, is held in reset by
> default. Until recently, the DMA controller was brought out of reset by the
> bootloader(i.e. U-Boot). But a recent change in U-Boot, the peripherals that
> are not used are held in reset and are left to Linux to bring them out of
> reset.
>
> Add a mechanism for getting the reset property and de-assert the primecell
> module from reset if found. This is a not a hard fail if the reset property
> is not present in the device tree node, so the driver will continue to probe.
>
> Because there are different variants of the controller that may have multiple
> reset signals, the code will find all reset(s) specified and de-assert them.
>
> Signed-off-by: Dinh Nguyen <dinguyen@...nel.org>
> ---
> v3: add a reset_control_put()
>     add error handling for -EPROBE_DEFER
> v2: move reset control to bus code
>     find all reset properties and de-assert them
> ---
>  drivers/amba/bus.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index 100e798a5c82..00e68ea416ca 100644
> --- a/drivers/amba/bus.c
> +++ b/drivers/amba/bus.c
> @@ -18,6 +18,7 @@
>  #include <linux/limits.h>
>  #include <linux/clk/clk-conf.h>
>  #include <linux/platform_device.h>
> +#include <linux/reset.h>
>
>  #include <asm/irq.h>
>
> @@ -401,6 +402,28 @@ static int amba_device_try_add(struct amba_device *dev, struct resource *parent)
>         ret = amba_get_enable_pclk(dev);
>         if (ret == 0) {
>                 u32 pid, cid;
> +               int count;
> +               struct reset_control *rstc;
> +
> +               /*
> +                * Find reset control(s) of the amba bus and de-assert them.
> +                */
> +               count = reset_control_get_count(&dev->dev);
> +               while (count > 0) {
> +                       rstc = of_reset_control_get_shared_by_index(dev->dev.of_node, count - 1);
> +                       if (IS_ERR(rstc)) {
> +                               if (PTR_ERR(rstc) == -EPROBE_DEFER) {
> +                                       ret = -EPROBE_DEFER;
> +                               } else {
> +                                       dev_err(&dev->dev, "Can't get amba reset!\n");
> +                               }
> +                               break;
> +                       } else {

You can remove the else here and save some indentation on the rest.

Otherwise,

Reviewed-by: Rob Herring <robh@...nel.org>


> +                               reset_control_deassert(rstc);
> +                               reset_control_put(rstc);
> +                               count--;
> +                       }
> +               }
>
>                 /*
>                  * Read pid and cid based on size of resource
> --
> 2.20.0
>