linux-kernel - Re: [PATCH v6 1/7] reset: mpfs: add non-auxiliary bus probing

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Message-ID: <4e3c3c3d6c1a0d2905a90e5f1c0b2cb8f67bc43b.camel@pengutronix.de>
Date: Thu, 30 Oct 2025 14:40:30 +0100
From: Philipp Zabel <p.zabel@...gutronix.de>
To: Conor Dooley <conor@...nel.org>, claudiu.beznea@...on.dev
Cc: Conor Dooley <conor.dooley@...rochip.com>, Daire McNamara
	 <daire.mcnamara@...rochip.com>, pierre-henry.moussay@...rochip.com, 
	valentina.fernandezalanis@...rochip.com, Michael Turquette
	 <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, Rob Herring
	 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	linux-riscv@...ts.infradead.org, linux-clk@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/7] reset: mpfs: add non-auxiliary bus probing

On Mi, 2025-10-29 at 16:11 +0000, Conor Dooley wrote:
> From: Conor Dooley <conor.dooley@...rochip.com>
> 
> While the auxiliary bus was a nice bandaid, and meant that re-writing
> the representation of the clock regions in devicetree was not required,
> it has run its course. The "mss_top_sysreg" region that contains the
> clock and reset regions, also contains pinctrl and an interrupt
> controller, so the time has come rewrite the devicetree and probe the
> reset controller from an mfd devicetree node, rather than implement
> those drivers using the auxiliary bus. Wanting to avoid propagating this
> naive/incorrect description of the hardware to the new pic64gx SoC is a
> major motivating factor here.
> 
> Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
> ---
> v6:
> - depend on MFD_SYSCON
> - return regmap_update_bits() result directly instead of an additional
>   return 0
> 
> v4:
> - Only use driver specific lock for non-regmap writes
> 
> v2:
> - Implement the request to use regmap_update_bits(). I found that I then
>   hated the read/write helpers since they were just bloat, so I ripped
>   them out. I replaced the regular spin_lock_irqsave() stuff with a
>   guard(spinlock_irqsave), since that's a simpler way of handling the two
>   different paths through such a trivial pair of functions.
> ---
>  drivers/reset/Kconfig      |  1 +
>  drivers/reset/reset-mpfs.c | 79 ++++++++++++++++++++++++++++++--------
>  2 files changed, 63 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/reset/Kconfig b/drivers/reset/Kconfig
> index 78b7078478d4..0ec4b7cd08d6 100644
> --- a/drivers/reset/Kconfig
> +++ b/drivers/reset/Kconfig
> @@ -200,6 +200,7 @@ config RESET_PISTACHIO
>  config RESET_POLARFIRE_SOC
>  	bool "Microchip PolarFire SoC (MPFS) Reset Driver"
>  	depends on MCHP_CLK_MPFS
> +	depends on MFD_SYSCON
>  	select AUXILIARY_BUS
>  	default MCHP_CLK_MPFS
>  	help
> diff --git a/drivers/reset/reset-mpfs.c b/drivers/reset/reset-mpfs.c
> index f6fa10e03ea8..25de7df55301 100644
> --- a/drivers/reset/reset-mpfs.c
> +++ b/drivers/reset/reset-mpfs.c
> @@ -7,13 +7,16 @@
>   *
>   */
>  #include <linux/auxiliary_bus.h>
> +#include <linux/cleanup.h>
>  #include <linux/delay.h>
>  #include <linux/io.h>
> +#include <linux/mfd/syscon.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
>  #include <linux/platform_device.h>
> -#include <linux/slab.h>
> +#include <linux/regmap.h>
>  #include <linux/reset-controller.h>
> +#include <linux/slab.h>
>  #include <dt-bindings/clock/microchip,mpfs-clock.h>
>  #include <soc/microchip/mpfs.h>
>  
> @@ -27,11 +30,14 @@
>  #define MPFS_SLEEP_MIN_US	100
>  #define MPFS_SLEEP_MAX_US	200
>  
> +#define REG_SUBBLK_RESET_CR	0x88u
> +
>  /* block concurrent access to the soft reset register */
>  static DEFINE_SPINLOCK(mpfs_reset_lock);
>  
>  struct mpfs_reset {
>  	void __iomem *base;
> +	struct regmap *regmap;
>  	struct reset_controller_dev rcdev;
>  };
>  
> @@ -46,41 +52,46 @@ static inline struct mpfs_reset *to_mpfs_reset(struct reset_controller_dev *rcde
>  static int mpfs_assert(struct reset_controller_dev *rcdev, unsigned long id)
>  {
>  	struct mpfs_reset *rst = to_mpfs_reset(rcdev);
> -	unsigned long flags;
>  	u32 reg;
>  
> -	spin_lock_irqsave(&mpfs_reset_lock, flags);
> +	if (rst->regmap)
> +		return regmap_update_bits(rst->regmap, REG_SUBBLK_RESET_CR, BIT(id), BIT(id));

This could use regmap_set_bits().

> +
> +	guard(spinlock_irqsave)(&mpfs_reset_lock);
>  
>  	reg = readl(rst->base);
>  	reg |= BIT(id);
>  	writel(reg, rst->base);

Since I've just seen this in the i.MX8ULP series [1], it would be
cleaner to convert the aux driver to regmap as well. The readl/writel()
code paths could be dropped then.

[1] https://lore.kernel.org/lkml/20251029135229.890-1-laurentiumihalcea111@gmail.com/

[...]
>  static int mpfs_deassert(struct reset_controller_dev *rcdev, unsigned long id)
>  {
>  	struct mpfs_reset *rst = to_mpfs_reset(rcdev);
> -	unsigned long flags;
>  	u32 reg;
>  
> -	spin_lock_irqsave(&mpfs_reset_lock, flags);
> +	if (rst->regmap)
> +		return regmap_update_bits(rst->regmap, REG_SUBBLK_RESET_CR, BIT(id), 0);

And this could use regmap_clear_bits().

regards
Philipp