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Date: Mon, 29 Aug 2016 19:23:01 -0500
From: Rob Herring <robh+dt@...nel.org>
To: Tony Lindgren <tony@...mide.com>
Cc: Frank Rowand <frowand.list@...il.com>,
Grant Likely <grant.likely@...aro.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
linux-omap <linux-omap@...r.kernel.org>,
Nishanth Menon <nm@...com>, Tero Kristo <t-kristo@...com>,
Tom Rini <trini@...sulko.com>
Subject: Re: [PATCHv2] of: Add generic handling for ePAPR 1.1 fail-sss states
On Mon, Aug 29, 2016 at 5:35 PM, Tony Lindgren <tony@...mide.com> wrote:
> We have devices that are in incomplete state, but still need to be
> probed to allow properly idling them for PM. Some examples are
> devices that are not pinned out on certain packages, or otherwise
> unusable on some SoCs.
>
> Setting status = "disabled" cannot be used for this case. Setting
> "disabled" makes Linux ignore these devices so they are not probed
> and can never get idled properly by Linux PM runtime.
>
> The proper way deal with the incomplete devices is to probe them,
> then allow the driver to check the state, and then disable or idle
> the device using PM runtime. To do this, we need to often enable
> the device and run some device specific code to idle the device.
>
> Also boards may have needs to disable and idle unused devices.
> This may be needed for example if all resources are not wired
> for a certain board variant.
>
> It seems we can use the ePAPR 1.1 status fail-sss to do this.
> Quoting "Table 2-4 Values for status property" we have "fail-sss":
>
> "Indicates that the device is not operational. A serious error was
> detected in the device and it is unlikely to become operational
> without repair. The sss portion of the value is specific to the
> device and indicates the error condition detected."
I had read this as 'sss' is just 3 characters, but I guess that doesn't matter.
> We can handle these fail states can be handled in a generic
> way. So let's introduce a generic status = "fail-" that
> describes a situation where a device driver probe should just
> shut down or idle the device if possible and then bail out.
> This allows the SoC variant and board specific dts files to set
> the status as needed.
>
> The suggested usage in a device driver probe is:
>
> static int foo_probe(struct platform_device *pdev)
> {
> int err;
> const char *status;
> ...
>
> pm_runtime_enable(&pdev->dev);
> pm_runtime_get_sync(&pdev->dev);
> pm_runtime_use_autosuspend(&pdev->dev);
> ...
>
> /* Configure device, load firmware, idle device */
> ...
>
> if (of_device_is_incomplete(pdev->dev.of_node, status)) {
&status
> if (!strcmp("hw-incomplete-pins", status)) {
> dev_info(&pdev->dev,
> "Unusable hardware: Not pinned out\n");
> err = -ENODEV;
> goto out;
> }
> if (!strcmp("hw-missing-daughter-card")) {
> err = -EPROBE_DEFER;
This implies we're going to change this on the fly? I guess
disabled->okay can already happen.
> goto out;
> }
> if (!strcmp("hw-buggy-dma")) {
> dev_warn(&pdev->dev,
> "Replace hardware for working DMA\n");
> }
> }
>
> /* Continue normal device probe */
> ...
>
> return 0;
>
> out:
> pm_runtime_dont_use_autosuspend(&pdev->dev);
> pm_runtime_put_sync(&pdev->dev);
> pm_runtime_disable(&pdev->dev);
>
> return err;
> }
>
> Cc: Nishanth Menon <nm@...com>
> Cc: Tero Kristo <t-kristo@...com>
> Cc: Tom Rini <trini@...sulko.com>
> Signed-off-by: Tony Lindgren <tony@...mide.com>
> ---
> Changes since v1 ([PATCH] of: Add generic handling for hardware incomplete
> fail state):
>
> - Make more generic as suggested by Frank but stick with
> "operational status of a device" approch most people seem
> to prefer that
>
> - Pass the failure status back to caller so the caller may
> attempt to handle the failure status
>
> - Improved the description with more examples
>
> drivers/of/base.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++---
> include/linux/of.h | 8 +++++++
> 2 files changed, 69 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index ff37f6d..4d39857 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -550,8 +550,8 @@ EXPORT_SYMBOL(of_machine_is_compatible);
> *
> * @device: Node to check for availability, with locks already held
> *
> - * Returns true if the status property is absent or set to "okay" or "ok",
> - * false otherwise
> + * Returns true if the status property is absent or set to "okay", "ok",
> + * or starting with "fail-", false otherwise
> */
> static bool __of_device_is_available(const struct device_node *device)
> {
> @@ -566,7 +566,8 @@ static bool __of_device_is_available(const struct device_node *device)
> return true;
>
> if (statlen > 0) {
> - if (!strcmp(status, "okay") || !strcmp(status, "ok"))
> + if (!strcmp(status, "okay") || !strcmp(status, "ok") ||
> + !strncmp(status, "fail-", 5))
> return true;
> }
>
> @@ -595,6 +596,63 @@ bool of_device_is_available(const struct device_node *device)
> EXPORT_SYMBOL(of_device_is_available);
>
> /**
> + * __of_device_is_incomplete - check if a device is incomplete
> + *
> + * @device: Node to check for partial failure with locks already held
> + * @status: Status string for optional handling of the fail-sss state
> + */
> +static bool __of_device_is_incomplete(const struct device_node *device,
> + const char **status)
> +{
> + const char *s, *m = "fail-";
> + int slen, mlen;
> +
> + if (!device)
> + return false;
> +
> + s = __of_get_property(device, "status", &slen);
You can use the string helper function here (or is the lock a problem?).
Overall, seems okay to me.
> + if (!s)
> + return false;
> +
> + mlen = strlen(m);
> + if (slen <= mlen)
> + return false;
> +
> + if (strncmp("fail-", s, mlen))
> + return false;
> +
> + *status = s + mlen;
> +
> + return true;
> +}
> +
> +/**
> + * of_device_is_incomplete - check if a device is incomplete
> + *
> + * @device: Node to check for partial failure
> + * @status: Status string for optional handling of the fail-sss state
> + *
> + * Returns true if the status property is set to "fail-sss",
> + * false otherwise. Fore more information, see fail-sss in ePAPR 1.1
> + * "Table 2-4 Values for status property".
> + *
> + * The caller can optionally try to handle the error based on the
> + * status string.
> + */
> +bool of_device_is_incomplete(const struct device_node *device,
> + const char **status)
> +{
> + unsigned long flags;
> + bool res;
> +
> + raw_spin_lock_irqsave(&devtree_lock, flags);
> + res = __of_device_is_incomplete(device, status);
> + raw_spin_unlock_irqrestore(&devtree_lock, flags);
> + return res;
> +}
> +EXPORT_SYMBOL(of_device_is_incomplete);
> +
> +/**
> * of_device_is_big_endian - check if a device has BE registers
> *
> * @device: Node to check for endianness
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 3d9ff8e..b593936 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -320,6 +320,8 @@ extern int of_device_is_compatible(const struct device_node *device,
> extern int of_device_compatible_match(struct device_node *device,
> const char *const *compat);
> extern bool of_device_is_available(const struct device_node *device);
> +extern bool of_device_is_incomplete(const struct device_node *device,
> + const char **status);
> extern bool of_device_is_big_endian(const struct device_node *device);
> extern const void *of_get_property(const struct device_node *node,
> const char *name,
> @@ -504,6 +506,12 @@ static inline bool of_device_is_available(const struct device_node *device)
> return false;
> }
>
> +static inline bool of_device_is_incomplete(const struct device_node *device,
> + const char **status)
> +{
> + return false;
> +}
> +
> static inline bool of_device_is_big_endian(const struct device_node *device)
> {
> return false;
> --
> 2.9.3
>
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