linux-kernel - Re: [PATCH] platform/chrome: cros_ec_lpc: Fix error code in cros_ec_lpc_mec_read

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Message-ID: <3226cba0-82c5-47a3-89da-01ffa935a9dc@moroto.mountain>
Date: Thu, 13 Jun 2024 20:57:24 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Ben Walsh <ben@...nut.com>
Cc: Benson Leung <bleung@...omium.org>, Tzung-Bi Shih <tzungbi@...nel.org>,
	Guenter Roeck <groeck@...omium.org>,
	chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] platform/chrome: cros_ec_lpc: Fix error code in
 cros_ec_lpc_mec_read_bytes()

On Thu, Jun 13, 2024 at 05:51:39PM +0100, Ben Walsh wrote:
> 
> Thanks for fixing this! Unfortunately `in_range` returns -EINVAL if
> length == 0 (see the definition of `fwk_ec_lpc_mec_in_range`). I'm sure
> this broke something in my testing, but I can't find what it was now.

I don't think fwk_ec_lpc_mec_in_range() is upstream.  This email is the
only reference I can find to it on the internet.

> 
> My original suggestion was to add a test for "length == 0" before the
> "in_range" test, then do the test as you have done. But we decided to
> defer this to a later, separate patch.
> 
> There's also a similar "in_range" test in `fwk_ec_lpc_mec_write_bytes`.
> 
> We could:
> 
>   1. Revert this and change the `data & EC_LPC_STATUS_BUSY_MASK` to
>   `res & EC_LPC_STATUS_BUSY_MASK`. This is the same logic as before the
>   negative error code change.
> 
>   or 2. Put in a check for length == 0.
> 
>   or 3. Change the logic in `fwk_ec_lpc_mec_in_range`. Although I'm not
>   sure what the correct answer is to "zero length is in range?"
> 
> I prefer option 2. What do you think?

diff --git a/drivers/platform/chrome/cros_ec_lpc_mec.c b/drivers/platform/chrome/cros_ec_lpc_mec.c
index dfad934e65ca..9bf74656164f 100644
--- a/drivers/platform/chrome/cros_ec_lpc_mec.c
+++ b/drivers/platform/chrome/cros_ec_lpc_mec.c
@@ -94,7 +94,7 @@ static void cros_ec_lpc_mec_emi_write_address(u16 addr,
 int cros_ec_lpc_mec_in_range(unsigned int offset, unsigned int length)
 {
 	if (length == 0)
-		return -EINVAL;
+		return 0;
 
 	if (WARN_ON(mec_emi_base == 0 || mec_emi_end == 0))
 		return -EINVAL;

But I don't like how subtle that is.  Probably adding a check for
for if (length == 0) to the  to cros_ec_lpc_mec_read_bytes() seems
like the best option.  I guess option 2 is the best option.

So far as I can see this is the only caller which passes "length == 0"
is in cros_ec_cmd_xfer_lpc().

        /* Read response and update checksum */
        ret = cros_ec_lpc_ops.read(EC_LPC_ADDR_HOST_PARAM, args.data_size,
                                                           ^^^^^^^^^^^^^^^
                                   msg->data);

regards,
dan carpenter