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mfd: cros_ec: Use a zero-length array for command data

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Commit 1b84f2a4cd ("mfd: cros_ec: Use fixed size arrays to transfer
data with the EC") modified the struct cros_ec_command fields to not
use pointers for the input and output buffers and use fixed length
arrays instead.

This change was made because the cros_ec ioctl API uses that struct
cros_ec_command to allow user-space to send commands to the EC and
to get data from the EC. So using pointers made the API not 64-bit
safe. Unfortunately this approach was not flexible enough for all
the use-cases since there may be a need to send larger commands
on newer versions of the EC command protocol.

So to avoid to choose a constant length that it may be too big for
most commands and thus wasting memory and CPU cycles on copy from
and to user-space or having a size that is too small for some big
commands, use a zero-length array that is both 64-bit safe and
flexible. The same buffer is used for both output and input data
so the maximum of these values should be used to allocate it.

Suggested-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
This commit is contained in:
Javier Martinez Canillas
2015-06-09 13:04:42 +02:00
committed by Lee Jones
parent bb03ffb96c
commit a841178445
10 changed files with 318 additions and 175 deletions
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6
include/linux/mfd/cros_ec.h
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@@ -42,8 +42,7 @@ enum {
* @outsize: Outgoing length in bytes
* @insize: Max number of bytes to accept from EC
* @result: EC's response to the command (separate from communication failure)
* @outdata: Outgoing data to EC
* @indata: Where to put the incoming data from EC
* @data: Where to put the incoming data from EC and outgoing data to EC
*/
struct cros_ec_command {
uint32_t version;
@@ -51,8 +50,7 @@ struct cros_ec_command {
uint32_t outsize;
uint32_t insize;
uint32_t result;
uint8_t outdata[EC_PROTO2_MAX_PARAM_SIZE];
uint8_t indata[EC_PROTO2_MAX_PARAM_SIZE];
uint8_t data[0];
};
/**