linux-kernel - Re: [PATCH v4 1/2] platform/x86: wmi: Support reading/writing 16 bit EC values

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Message-ID: <a6152da8-5f3a-458b-bc48-4bc654677ece@linux.intel.com>
Date: Sat, 9 Mar 2024 09:07:30 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: Armin Wolf <W_Armin@....de>, hdegoede@...hat.com,
 ilpo.jarvinen@...ux.intel.com
Cc: rafael@...nel.org, lenb@...nel.org, mario.limonciello@....com,
 linux-acpi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] platform/x86: wmi: Support reading/writing 16 bit
 EC values


On 3/8/24 1:05 PM, Armin Wolf wrote:
> The ACPI EC address space handler currently only supports
> reading/writing 8 bit values. Some firmware implementations however
> want to access for example 16 bit values, which is prefectly legal
> according to the ACPI spec.
>
> Add support for reading/writing such values.
>
> Tested on a Dell Inspiron 3505 and a Asus Prime B650-Plus.
>
> Signed-off-by: Armin Wolf <W_Armin@....de>
> ---
> Changes since v3:
> - change type of variable i to size_t
>
> Changes since v2:
> - fix address overflow check
>
> Changes since v1:
> - use BITS_PER_BYTE
> - validate that number of bytes to read/write does not overflow the
>   address
> ---
>  drivers/platform/x86/wmi.c | 49 ++++++++++++++++++++++++++++++--------
>  1 file changed, 39 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
> index 1920e115da89..d9bf6d452b3a 100644
> --- a/drivers/platform/x86/wmi.c
> +++ b/drivers/platform/x86/wmi.c
> @@ -1153,6 +1153,34 @@ static int parse_wdg(struct device *wmi_bus_dev, struct platform_device *pdev)
>  	return 0;
>  }
>
> +static int ec_read_multiple(u8 address, u8 *buffer, size_t bytes)
> +{
> +	size_t i;
> +	int ret;
> +
> +	for (i = 0; i < bytes; i++) {
> +		ret = ec_read(address + i, &buffer[i]);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	return 0;
> +}

Why not use ec_transaction?

> +
> +static int ec_write_multiple(u8 address, u8 *buffer, size_t bytes)
> +{
> +	size_t i;
> +	int ret;
> +
> +	for (i = 0; i < bytes; i++) {
> +		ret = ec_write(address + i, buffer[i]);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	return 0;
> +}

Same as above.
> +
>  /*
>   * WMI can have EmbeddedControl access regions. In which case, we just want to
>   * hand these off to the EC driver.
> @@ -1162,27 +1190,28 @@ acpi_wmi_ec_space_handler(u32 function, acpi_physical_address address,
>  			  u32 bits, u64 *value,
>  			  void *handler_context, void *region_context)
>  {
> -	int result = 0;
> -	u8 temp = 0;
> +	int bytes = bits / BITS_PER_BYTE;
> +	int ret;
> +
> +	if (!value)
> +		return AE_NULL_ENTRY;
>
> -	if ((address > 0xFF) || !value)
> +	if (!bytes || bytes > sizeof(*value))
>  		return AE_BAD_PARAMETER;
>
> -	if (function != ACPI_READ && function != ACPI_WRITE)
> +	if (address > U8_MAX || address + bytes - 1 > U8_MAX)
>  		return AE_BAD_PARAMETER;
>
> -	if (bits != 8)

Since you want to support only 16 bit reads/writes, can you check for >16

> +	if (function != ACPI_READ && function != ACPI_WRITE)
>  		return AE_BAD_PARAMETER;
>
>  	if (function == ACPI_READ) {
> -		result = ec_read(address, &temp);
> -		*value = temp;
> +		ret = ec_read_multiple(address, (u8 *)value, bytes);
>  	} else {
> -		temp = 0xff & *value;
> -		result = ec_write(address, temp);
> +		ret = ec_write_multiple(address, (u8 *)value, bytes);
>  	}
>
> -	switch (result) {
> +	switch (ret) {
>  	case -EINVAL:
>  		return AE_BAD_PARAMETER;
>  	case -ENODEV:
> --
> 2.39.2
>
>
-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer