linux-kernel - Re: [RFC PATCH 7/8] firewire: core: detect model name for legacy layout of configuration ROM

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Date: Mon, 18 Dec 2023 21:50:26 +0900
From: Takashi Sakamoto <o-takashi@...amocchi.jp>
To: Adam Goldman <adamg@...ox.com>
Cc: linux1394-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 7/8] firewire: core: detect model name for legacy
 layout of configuration ROM

Hi,

On Mon, Dec 18, 2023 at 02:04:52AM -0800, Adam Goldman wrote:
> Hi,
> 
> On Sun, Dec 17, 2023 at 07:30:10PM +0900, Takashi Sakamoto wrote:
> > -	ret = fw_csr_string(dir, attr->key, buf, bufsize);
> > +	for (i = 0; i < ARRAY_SIZE(directories) && directories[i]; ++i)
> > +		ret = fw_csr_string(directories[i], attr->key, buf, bufsize);
> 
> I believe this is incorrect. If the attribute is in the first directory 
> searched, the loop will continue. The second loop iteration will set ret 
> to -ENOENT because the attribute isn't in the second directory. Then 
> show_text_leaf will return -ENOENT even though the attribute existed.

Exactly. It is a bug.

I think we can solve it by aligning the pointers of directory in reverse
order within the array, like:

```
diff --git a/drivers/firewire/core-device.c b/drivers/firewire/core-device.c
index d3fc3270a00b..adae3268291f 100644
--- a/drivers/firewire/core-device.c
+++ b/drivers/firewire/core-device.c
@@ -326,13 +326,17 @@ static ssize_t show_text_leaf(struct device *dev,
                directories[0] = fw_unit(dev)->directory;
        } else {
                const u32 *root_directory = fw_device(dev)->config_rom + ROOT_DIR_OFFSET;
+               const u32 *vendor_directory = search_directory(root_directory, CSR_VENDOR);

-               directories[0] = root_directory;
-
-               // Legacy layout of configuration ROM described in Annex 1 of 'Configuration ROM
-               // for AV/C Devices 1.0 (December 12, 2000, 1394 Trading Association, TA Document
-               // 1999027)'.
-               directories[1] = search_directory(root_directory, CSR_VENDOR);
+               if (!vendor_directory) {
+                       directories[0] = root_directory;
+               } else {
+                       // Legacy layout of configuration ROM described in Annex 1 of
+                       // 'Configuration ROM for AV/C Devices 1.0 (December 12, 2000, 1394
+                       // Trading Association, TA Document 1999027)'.
+                       directories[0] = vendor_directory;
+                       directories[1] = root_directory;
+               }
        }

        if (buf) {
@@ -342,8 +346,11 @@ static ssize_t show_text_leaf(struct device *dev,
                bufsize = 1;
        }

-       for (i = 0; i < ARRAY_SIZE(directories) && directories[i]; ++i)
+       for (i = 0; i < ARRAY_SIZE(directories) && directories[i]; ++i) {
                ret = fw_csr_string(directories[i], attr->key, buf, bufsize);
+               if (ret >= 0)
+                       break;
+       }

        if (ret >= 0) {
                /* Strip trailing whitespace and add newline. */
```

Thanks

Takashi Sakamoto