linux-kernel - Re: [PATCHv5] drivers/amba: add reset control to amba bus probe

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Message-ID: <1566834704.3842.7.camel@pengutronix.de>
Date:   Mon, 26 Aug 2019 17:51:44 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Dinh Nguyen <dinguyen@...nel.org>, linux-kernel@...r.kernel.org
Cc:     devicetree@...r.kernel.org, robh@...nel.org, linux@...linux.org.uk,
        frowand.list@...il.com, keescook@...omium.org, anton@...msg.org,
        ccross@...roid.com, tony.luck@...el.com,
        daniel.thompson@...aro.org, linus.walleij@...aro.org,
        manivannan.sadhasivam@...aro.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv5] drivers/amba: add reset control to amba bus probe

On Mon, 2019-08-26 at 10:42 -0500, Dinh Nguyen 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 properti
> 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>
> Reviewed-by: Rob Herring <robh@...nel.org>
> ---
> v5: use of_reset_control_array_get_optional_shared()
> v4: cleaned up indentation in loop
>     fix up a few checkpatch warnings
>     add Reviewed-by:
> v3: add a reset_control_put()
>     add error handling
> v2: move reset control to bus code
>     find all reset properties and de-assert them
> ---
>  drivers/amba/bus.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
> index 100e798a5c82..f8a7cb74c3cf 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 +402,24 @@ 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_array_get_optional_shared(dev->dev.of_node);

You can drop the loop, the rstc returned by of_reset_control_array_get()
already controls all resets together.

regards
Philipp