linux-kernel - Re: [PATCH v7 05/24] wfx: add main.c/main.h

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Message-ID: <87zgrl86cx.fsf@codeaurora.org>
Date:   Thu, 07 Oct 2021 13:41:18 +0300
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Jérôme Pouiller <jerome.pouiller@...abs.com>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S . Miller" <davem@...emloft.net>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-mmc@...r.kernel.org,
        Pali Rohár <pali@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v7 05/24] wfx: add main.c/main.h

Jérôme Pouiller <jerome.pouiller@...abs.com> writes:

>> >> >> I'm not really fond of having this kind of ASCII based parser in the
>> >> >> kernel. Do you have an example compressed file somewhere?
>> >> >
>> >> > An example of uncompressed configuration file can be found here[1]. Once
>> >> > compressed with [2], you get:
>> >> >
>> >> >     {a:{a:4,b:1},b:{a:{a:4,b:0,c:0,d:0,e:A},b:{a:4,b:0,c:0,d:0,e:B},c:{a:4,b:0,c:0,d:0,e:C},d:{a:4,b:0,c:0,d:0,e:D},e:{a:4,b:0,c:0,d:0,e:E},f:{a:4,b:0,c:0,d:0,e:F},g:{a:4,b:0,c:0,d:0,e:G},h:{a:4,b:0,c:0,d:0,e:H},i:{a:4,b:0,c:0,d:0,e:I},j:{a:4,b:0,c:0,d:0,e:J},k:{a:4,b:0,c:0,d:0,e:K},l:{a:4,b:0,c:0,d:1,e:L},m:{a:4,b:0,c:0,d:1,e:M}},c:{a:{a:4},b:{a:6},c:{a:6,c:0},d:{a:6},e:{a:6},f:{a:6}},e:{b:0,c:1},h:{e:0,a:50,b:0,d:0,c:[{a:1,b:[0,0,0,0,0,0]},{a:2,b:[0,0,0,0,0,0]},{a:[3,9],b:[0,0,0,0,0,0]},{a:A,b:[0,0,0,0,0,0]},{a:B,b:[0,0,0,0,0,0]},{a:[C,D],b:[0,0,0,0,0,0]},{a:E,b:[0,0,0,0,0,0]}]},j:{a:0,b:0}}
>> >>
>> >> So what's the grand idea with this braces format? I'm not getting it.
>> >
>> >   - It allows to describe a tree structure
>> >   - It is ascii (easy to dump, easy to copy-paste)
>> >   - It is small (as I explain below, size matters)
>> >   - Since it is similar to JSON, the structure is obvious to many people
>> >
>> > Anyway, I am not the author of that and I have to deal with it.
>> 
>> I'm a supported for JSON like formats, flexibility and all that. But
>> they belong to user space, not kernel.
>> 
>> >> Usually the drivers just consider this kind of firmware configuration
>> >> data as a binary blob and dump it to the firmware, without knowing what
>> >> the data contains. Can't you do the same?
>> >
>> > [I didn't had received this mail :( ]
>> >
>> > The idea was also to send it as a binary blob. However, the firmware use
>> > a limited buffer (1500 bytes) to parse it. In most of case the PDS exceeds
>> > this size. So, we have to split the PDS before to send it.
>> >
>> > Unfortunately, we can't split it anywhere. The PDS is a tree structure and
>> > the firmware expects to receive a well formatted tree.
>> >
>> > So, the easiest way to send it to the firmware is to split the tree
>> > between each root nodes and send each subtree separately (see also the
>> > comment above wfx_send_pds()).
>> >
>> > Anyway, someone has to cook this configuration before to send it to the
>> > firmware. This could be done by a script outside of the kernel. Then we
>> > could change the input format to simplify a bit the processing in the
>> > kernel.
>> 
>> I think a binary file with TLV format would be much better, but I'm sure
>> there also other good choises.
>> 
>> > However, the driver has already some users and I worry that changing
>> > the input format would lead to a mess.
>> 
>> You can implement a script which converts the old format to the new
>> format. And you can use different naming scheme in the new format so
>> that we don't accidentally load the old format. And even better if you
>> add a some kind of signature in the new format and give a proper error
>> from the driver if it doesn't match.
>
> Ok. I am going to change the input format. I think the new function is
> going to look like:
>
> int wfx_send_pds(struct wfx_dev *wdev, u8 *buf, size_t buf_len)
> {
> 	int ret;
> 	int start = 0;
>
> 	if (buf[start] != '{') {
> 		dev_err(wdev->dev, "valid PDS start with '{'. Did you forget to compress it?\n");
> 		return -EINVAL;
> 	}
> 	while (start < buf_len) {
> 		len = strnlen(buf + start, buf_len - start);
> 		if (len > WFX_PDS_MAX_SIZE) {
> 			dev_err(wdev->dev, "PDS chunk is too big (legacy format?)\n");
> 			return -EINVAL;
> 		}
> 		dev_dbg(wdev->dev, "send PDS '%s'\n", buf + start);
> 		ret = wfx_hif_configuration(wdev, buf + start, len);
> 		/* FIXME: Add error handling here */
> 		start += len;
> 	}
> 	return 0;

Did you read at all what I wrote above? Please ditch the ASCII format
completely.

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