linux-kernel - Re: [PATCH 4/8] platform/chrome: cros_ec_chardev: Use cros_ec_cmd_xfer

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Message-ID: <20200225195519.GC11971@google.com>
Date:   Tue, 25 Feb 2020 11:55:19 -0800
From:   Prashant Malani <pmalani@...omium.org>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:     linux-kernel@...r.kernel.org,
        Collabora Kernel ML <kernel@...labora.com>,
        groeck@...omium.org, bleung@...omium.org, dtor@...omium.org,
        gwendal@...omium.org
Subject: Re: [PATCH 4/8] platform/chrome: cros_ec_chardev: Use
 cros_ec_cmd_xfer_status helper

Hi Enric,

On Thu, Feb 20, 2020 at 04:58:55PM +0100, Enric Balletbo i Serra wrote:
> This patch makes use of cros_ec_cmd_xfer_status() instead of
> cros_ec_cmd_xfer(). In this case the change is trivial and the only
> reason to do it is because we want to make cros_ec_cmd_xfer() a private
> function for the EC protocol and let people only use the
> cros_ec_cmd_xfer_status() to return Linux standard error codes.
> 
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> ---
> 
>  drivers/platform/chrome/cros_ec_chardev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/chrome/cros_ec_chardev.c b/drivers/platform/chrome/cros_ec_chardev.c
> index c65e70bc168d..b51ab24055f3 100644
> --- a/drivers/platform/chrome/cros_ec_chardev.c
> +++ b/drivers/platform/chrome/cros_ec_chardev.c
> @@ -301,7 +301,7 @@ static long cros_ec_chardev_ioctl_xcmd(struct cros_ec_dev *ec, void __user *arg)
>  	}
>  
>  	s_cmd->command += ec->cmd_offset;
> -	ret = cros_ec_cmd_xfer(ec->ec_dev, s_cmd);
> +	ret = cros_ec_cmd_xfer_status(ec->ec_dev, s_cmd);

One issue I see here is that if we were to later convert
cros_ec_cmd_xfer_status() to cros_ec_cmd(), we would lose the
s_cmd->result value, since I was hoping to avoid returning msg->result
via a pointer parameter. I don't know if userspace actually uses that, but I
am assuming it does.

So, should cros_ec_cmd() keep the *result pointer like so ?:

int cros_ec_cmd(struct cros_ec_device *ec, u32 version, u32 command,
               void *outdata, u32 outsize, void *indata, u32 insize, u32 *result);

This way, we can manually re-populate s_cmd->result with |*result|.

Or, should we drop msg->result while returning s_cmd to userspace? I am
guessing the answer is no, but thought I'd check with you first.

Best regards,


>  	/* Only copy data to userland if data was received. */
>  	if (ret < 0)
>  		goto exit;
> -- 
> 2.25.0
>