Message-ID: <20241115103434410-0800.eberman@hu-eberman-lv.qualcomm.com>
Date: Fri, 15 Nov 2024 11:08:13 -0800
From: Elliot Berman <quic_eberman@...cinc.com>
To: Lorenzo Pieralisi <lpieralisi@...nel.org>
CC: Bjorn Andersson <andersson@...nel.org>,
        Sebastian Reichel
	<sre@...nel.org>, Rob Herring <robh@...nel.org>,
        Conor Dooley
	<conor+dt@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Andy Yan
	<andy.yan@...k-chips.com>,
        Mark Rutland <mark.rutland@....com>,
        "Bartosz
 Golaszewski" <bartosz.golaszewski@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, <cros-qcom-dts-watchers@...omium.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Konrad Dybcio
	<konradybcio@...nel.org>,
        Satya Durga Srinivasu Prabhala
	<quic_satyap@...cinc.com>,
        Melody Olvera <quic_molvera@...cinc.com>,
        Shivendra Pratap <quic_spratap@...cinc.com>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Stephen Boyd
	<swboyd@...omium.org>, <linux-pm@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v8 3/6] firmware: psci: Read and use vendor reset types

On Fri, Nov 15, 2024 at 02:51:16PM +0100, Lorenzo Pieralisi wrote:
> On Thu, Nov 07, 2024 at 03:38:27PM -0800, Elliot Berman wrote:
> > SoC vendors have different types of resets and are controlled through
> > various registers. For instance, Qualcomm chipsets can reboot to a
> > "download mode" that allows a RAM dump to be collected. Another example
> > is they also support writing a cookie that can be read by bootloader
> > during next boot. PSCI offers a mechanism, SYSTEM_RESET2, for these
> > vendor reset types to be implemented without requiring drivers for every
> > register/cookie.
> > 
> > Add support in PSCI to statically map reboot mode commands from
> > userspace to a vendor reset and cookie value using the device tree.
> > 
> > A separate initcall is needed to parse the devicetree, instead of using
> > psci_dt_init because mm isn't sufficiently set up to allocate memory.
> 
> Nit: information below this point is more a cover letter than for the
> commit log.
> 
> > Reboot mode framework is close but doesn't quite fit with the
> > design and requirements for PSCI SYSTEM_RESET2. Some of these issues can
> > be solved but doesn't seem reasonable in sum:
> >  1. reboot mode registers against the reboot_notifier_list, which is too
> >     early to call SYSTEM_RESET2. PSCI would need to remember the reset
> >     type from the reboot-mode framework callback and use it
> >     psci_sys_reset.
> >  2. reboot mode assumes only one cookie/parameter is described in the
> >     device tree. SYSTEM_RESET2 uses 2: one for the type and one for
> >     cookie.
> >  3. psci cpuidle driver already registers a driver against the
> >     arm,psci-1.0 compatible. Refactoring would be needed to have both a
> >     cpuidle and reboot-mode driver.
> > 
> > Tested-by: Florian Fainelli <florian.fainelli@...adcom.com>
> > Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>
> > ---
> >  drivers/firmware/psci/psci.c | 104 +++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 104 insertions(+)
> > 
> > diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> > index 2328ca58bba61fdb677ac20a1a7447882cd0cf22..e60e3f8749c5a6732c51d23a2c1f453361132d9a 100644
> > --- a/drivers/firmware/psci/psci.c
> > +++ b/drivers/firmware/psci/psci.c
> > @@ -79,6 +79,14 @@ struct psci_0_1_function_ids get_psci_0_1_function_ids(void)
> >  static u32 psci_cpu_suspend_feature;
> >  static bool psci_system_reset2_supported;
> >  
> > +struct psci_reset_param {
> > +	const char *mode;
> > +	u32 reset_type;
> > +	u32 cookie;
> > +};
> > +static struct psci_reset_param *psci_reset_params __ro_after_init;
> > +static size_t num_psci_reset_params __ro_after_init;
> > +
> >  static inline bool psci_has_ext_power_state(void)
> >  {
> >  	return psci_cpu_suspend_feature &
> > @@ -305,9 +313,38 @@ static int get_set_conduit_method(const struct device_node *np)
> >  	return 0;
> >  }
> >  
> > +static void psci_vendor_system_reset2(const char *cmd)
> > +{
> > +	unsigned long ret;
> > +	size_t i;
> > +
> > +	for (i = 0; i < num_psci_reset_params; i++) {
> > +		if (!strcmp(psci_reset_params[i].mode, cmd)) {
> > +			ret = invoke_psci_fn(PSCI_FN_NATIVE(1_1, SYSTEM_RESET2),
> > +					     psci_reset_params[i].reset_type,
> > +					     psci_reset_params[i].cookie, 0);
> > +			/*
> > +			 * if vendor reset fails, log it and fall back to
> > +			 * architecture reset types
> > +			 */
> > +			pr_err("failed to perform reset \"%s\": %ld\n", cmd,
> > +			       (long)ret);
> > +			return;
> > +		}
> > +	}
> > +}
> > +
> >  static int psci_sys_reset(struct notifier_block *nb, unsigned long action,
> >  			  void *data)
> >  {
> > +	/*
> > +	 * try to do the vendor system_reset2
> > +	 * If the reset fails or there wasn't a match on the command,
> > +	 * fall back to architectural resets
> > +	 */
> > +	if (data && num_psci_reset_params)
> > +		psci_vendor_system_reset2(data);
> > +
> >  	if ((reboot_mode == REBOOT_WARM || reboot_mode == REBOOT_SOFT) &&
> >  	    psci_system_reset2_supported) {
> 
> This is a mess. To issue architectural warm reset we check reboot_mode,
> for vendor resets we ignore it - there is no rationale, that's the point
> I am making.

If I expand the comment to:


 * try todo the vendor system_reset2
 * If the reset fails or there wasn't a match on the command,
 * fall back to architectural resets.
 * Ignore reboot_mode enum to behave like setting a cookie, which don't
 * care about the reboot_mode.


Help to address this concern?

> 
> Also see my question on the other thread re: user space and reset
> "modes".
> 
> I appreciate we are not making progress but I don't want to pick up
> the pieces later after merging this code - it is unclear to me what's
> the best path forward - I would like to understand how other
> platforms/arches behave in this respect.
> 

I went through the couple hundred drivers which register reboot and
restart handlers. The majority don't care about reboot command nor
reboot_mode enum. The few that do:

Two drivers which I could find which care about the reboot command don't
look at the reboot_mode argument.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/firmware/efi/efibc.c?h=v6.11#n35
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/power/reset/reboot-mode.c?h=v6.11#n42

One driver looks at the reboot command overrides the reboot_mode
argument:

[3]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/watchdog/pnx4008_wdt.c?h=v6.11#n125

I wasn't able to find any platform/arches which check the reboot_mode
before reading the reboot command.

> >  		/*
> > @@ -750,6 +787,73 @@ static const struct of_device_id psci_of_match[] __initconst = {
> >  	{},
> >  };
> >  
> > +#define REBOOT_PREFIX "mode-"
> > +
> > +static int __init psci_init_system_reset2_modes(void)
> > +{
> > +	const size_t len = strlen(REBOOT_PREFIX);
> > +	struct psci_reset_param *param;
> > +	struct device_node *psci_np __free(device_node) = NULL;
> > +	struct device_node *np __free(device_node) = NULL;
> > +	struct property *prop;
> > +	size_t count = 0;
> > +	u32 magic[2];
> > +	int num;
> > +
> > +	if (!psci_system_reset2_supported)
> > +		return 0;
> > +
> > +	psci_np = of_find_matching_node(NULL, psci_of_match);
> > +	if (!psci_np)
> > +		return 0;
> > +
> > +	np = of_find_node_by_name(psci_np, "reset-types");
> > +	if (!np)
> > +		return 0;
> > +
> > +	for_each_property_of_node(np, prop) {
> > +		if (strncmp(prop->name, REBOOT_PREFIX, len))
> > +			continue;
> > +		num = of_property_count_u32_elems(np, prop->name);
> > +		if (num != 1 && num != 2)
> > +			continue;
> > +
> > +		count++;
> > +	}
> > +
> > +	param = psci_reset_params =
> > +		kcalloc(count, sizeof(*psci_reset_params), GFP_KERNEL);
> > +	if (!psci_reset_params)
> > +		return -ENOMEM;
> > +
> > +	for_each_property_of_node(np, prop) {
> > +		if (strncmp(prop->name, REBOOT_PREFIX, len))
> > +			continue;
> > +
> > +		param->mode = kstrdup_const(prop->name + len, GFP_KERNEL);
> 
> FWIW - I think you need to keep the logic in the previous loop into account
> because that's what is used to allocate param, it is not a given that
> param is valid at this stage if I am not mistaken - the previous loop
> checked:
> 
> 	num = of_property_count_u32_elems(np, prop->name);
> 	if (num != 1 && num != 2)
> 		continue;

of_property_read_variable_u32_array() performs effectively the same
check.  It returns -EOVERFLOW if it couldn't find enough (== 0) or too
many values (>2). I currently have the added bonus of complaining in
dmesg about the bad reboot mode property, instead of silently ignoring.

- Elliot

> > +		if (!param->mode)
> > +			continue;
> > +
> > +		num = of_property_read_variable_u32_array(np, prop->name, magic,
> > +							  1, ARRAY_SIZE(magic));
> > +		if (num < 0) {
> > +			pr_warn("Failed to parse vendor reboot mode %s\n",
> > +				param->mode);
> > +			kfree_const(param->mode);
> > +			continue;
> > +		}
> > +
> > +		/* Force reset type to be in vendor space */
> > +		param->reset_type = PSCI_1_1_RESET_TYPE_VENDOR_START | magic[0];
> > +		param->cookie = num > 1 ? magic[1] : 0;
> > +		param++;
> > +		num_psci_reset_params++;
> > +	}
> > +
> > +	return 0;
> > +}
> > +arch_initcall(psci_init_system_reset2_modes);
> > +
> >  int __init psci_dt_init(void)
> >  {
> >  	struct device_node *np;
> > 
> > -- 
> > 2.34.1
> > 

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