linux-kernel - Re: [PATCH v2 6/7] platform/chrome: cros_ec_spi: drop unneeded BUG

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Message-ID: <CABXOdTdxZGQb4sLaBQU1eU9qRj_xgA8qrRmuCfavLqXpwG39=g@mail.gmail.com>
Date:   Fri, 13 May 2022 06:19:29 -0700
From:   Guenter Roeck <groeck@...gle.com>
To:     Tzung-Bi Shih <tzungbi@...nel.org>
Cc:     Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        chrome-platform@...ts.linux.dev,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 6/7] platform/chrome: cros_ec_spi: drop unneeded BUG_ON()

On Thu, May 12, 2022 at 9:42 PM Tzung-Bi Shih <tzungbi@...nel.org> wrote:
>
> In the context, the following conditions are always false:
>
> - `todo` < 0
> Suppose that EC_SPI_FRAME_START is found at the last byte of transfer.
>
> In the case, `ptr` == `end` - 1.  As a result, `todo` must be 0.
>
> - `todo` > `ec_dev->din_size`
> Suppose that there is no preamble bytes.  EC_SPI_FRAME_START is found at
> the first byte of transfer.
>
> In the case, `end` == `ptr` + EC_MSG_PREAMBLE_COUNT.
> As a result, `todo` == EC_MSG_PREAMBLE_COUNT - 1.
> However, it already checked `ec_dev->din_size` < EC_MSG_PREAMBLE_COUNT at
> the beginning of function.
>
> Drop the unneeded BUG_ON().
>
> Signed-off-by: Tzung-Bi Shih <tzungbi@...nel.org>

Reviewed-by: Guenter Roeck <groeck@...omium.org>

> ---
> Changes from v1:
> - Separate from the original 6th patch.
> - Drop the BUG_ON() instead of returning -EINVAL.
>
>  drivers/platform/chrome/cros_ec_spi.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/drivers/platform/chrome/cros_ec_spi.c b/drivers/platform/chrome/cros_ec_spi.c
> index 589f18e9537d..5264615f46af 100644
> --- a/drivers/platform/chrome/cros_ec_spi.c
> +++ b/drivers/platform/chrome/cros_ec_spi.c
> @@ -237,7 +237,6 @@ static int cros_ec_spi_receive_packet(struct cros_ec_device *ec_dev,
>          * start of our buffer
>          */
>         todo = end - ++ptr;
> -       BUG_ON(todo < 0 || todo > ec_dev->din_size);
>         todo = min(todo, need_len);
>         memmove(ec_dev->din, ptr, todo);
>         ptr = ec_dev->din + todo;
> @@ -345,7 +344,6 @@ static int cros_ec_spi_receive_response(struct cros_ec_device *ec_dev,
>          * start of our buffer
>          */
>         todo = end - ++ptr;
> -       BUG_ON(todo < 0 || todo > ec_dev->din_size);
>         todo = min(todo, need_len);
>         memmove(ec_dev->din, ptr, todo);
>         ptr = ec_dev->din + todo;
> --
> 2.36.0.550.gb090851708-goog
>