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List:       linux-efi
Subject:    Re: [PATCH] efi/apple-properties: Reinstate support for boolean properties
From:       Andy Shevchenko <andriy.shevchenko () linux ! intel ! com>
Date:       2020-12-28 14:53:57
Message-ID: 20201228145357.GY4077 () smile ! fi ! intel ! com
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On Sun, Dec 27, 2020 at 03:30:32PM +0100, Lukas Wunner wrote:
> Since commit 4466bf82821b ("efi/apple-properties: use
> PROPERTY_ENTRY_U8_ARRAY_LEN"), my MacBook Pro issues a -ENODATA error
> when trying to assign EFI properties to the discrete GPU:
> 
> pci 0000:01:00.0: assigning 56 device properties
> pci 0000:01:00.0: error -61 assigning properties
> 
> That's because some of the properties have no value.  They're booleans
> whose presence can be checked by drivers, e.g. "use-backlight-blanking".
> 
> Commit 6e98503dba64 ("efi/apple-properties: Remove redundant attribute
> initialization from unmarshal_key_value_pairs()") used a trick to store
> such booleans as u8 arrays (which is the data type used for all other
> EFI properties on Macs):  It cleared the property_entry's "is_array"
> flag, thereby denoting that the value is stored inline in the
> property_entry.
> 
> Commit 4466bf82821b erroneously removed that trick.  It was probably a
> little fragile to begin with.

Thanks for spotting this!
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
One nitpick below, though.

> Reinstate support for boolean properties by explicitly using the
> PROPERTY_ENTRY_BOOL() initializer for properties with zero-length value.
> 
> Fixes: 4466bf82821b ("efi/apple-properties: use PROPERTY_ENTRY_U8_ARRAY_LEN")
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> Cc: stable@vger.kernel.org # v5.5+
> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  drivers/firmware/efi/apple-properties.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/firmware/efi/apple-properties.c b/drivers/firmware/efi/apple-properties.c
> index 34f53d898acb..0f37877db641 100644
> --- a/drivers/firmware/efi/apple-properties.c
> +++ b/drivers/firmware/efi/apple-properties.c
> @@ -3,8 +3,9 @@
>   * apple-properties.c - EFI device properties on Macs
>   * Copyright (C) 2016 Lukas Wunner <lukas@wunner.de>
>   *
> - * Note, all properties are considered as u8 arrays.
> - * To get a value of any of them the caller must use device_property_read_u8_array().
> + * Properties are stored either as:
> + * booleans which can be queried with device_property_present() or
> + * u8 arrays which can be retrieved with device_property_read_u8_array().
>   */
>  
>  #define pr_fmt(fmt) "apple-properties: " fmt
> @@ -88,8 +89,11 @@ static void __init unmarshal_key_value_pairs(struct dev_header *dev_header,
>  
>  		entry_data = ptr + key_len + sizeof(val_len);
>  		entry_len = val_len - sizeof(val_len);
> -		entry[i] = PROPERTY_ENTRY_U8_ARRAY_LEN(key, entry_data,
> -						       entry_len);
> +		if (!entry_len)
> +			entry[i] = PROPERTY_ENTRY_BOOL(key);
> +		else
> +			entry[i] = PROPERTY_ENTRY_U8_ARRAY_LEN(key, entry_data,
> +							       entry_len);

Can we use positive conditional, i.e.

		if (entry_len)
			entry[i] = PROPERTY_ENTRY_U8_ARRAY_LEN(key, entry_data,
							       entry_len);
		else
			entry[i] = PROPERTY_ENTRY_BOOL(key);
?

>  		if (dump_properties) {
>  			dev_info(dev, "property: %s\n", key);
>  			print_hex_dump(KERN_INFO, pr_fmt(), DUMP_PREFIX_OFFSET,
> -- 
> 2.29.2
> 

-- 
With Best Regards,
Andy Shevchenko


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