Re: [PATCH v8 3/6] firmware: psci: Read and use vendor reset types

[Elliot Berman <quic_eberman@quicinc.com>]

On Mon, Nov 18, 2024 at 01:26:48PM +0100, Lorenzo Pieralisi wrote:
> On Fri, Nov 15, 2024 at 11:08:13AM -0800, Elliot Berman wrote:
> > 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@broadcom.com>
> > > > Signed-off-by: Elliot Berman <quic_eberman@quicinc.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.
> 
> /*
>  * Check if the system supports vendor resets and issue
>  * SYSTEM_RESET2 if the reboot command matches a vendor reset.
>  * Ignore reboot_mode and execute SYSTEM_RESET2 with type and
>  * cookie as defined by the firmware bindings.
>  *
>  * If the reset fails or there is not a match for the command
>  * fall back to architectural resets; reset type detection in
>  * this case will be done using reboot_mode.
>  */
> 
> ?
> 
> > Help to address this concern?
> 
> Not entirely, sorry, I will get back to this.
> 
> > > 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
> 
> Thanks for doing that, that helps.
> 
> > 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.
> 
> Right but we are dereferencing param (param->mode) before carrying out that
> check.
> 

Ah, right, I see the problem. I'll send out another version after
settling on the other part of the discussion!

Thanks,
Elliot