Subject: Re: [PATCH v7 05/24] wfx: add main.c/main.h

From: Jérôme Pouiller <[email-masked]>
Date: Thu, 07 Oct 2021 12:00:18 +0200

On Thursday 7 October 2021 10:35:43 CEST Kalle Valo wrote:
> Jérôme Pouiller <[email-masked]> writes:
> > On Friday 1 October 2021 14:18:04 CEST Kalle Valo wrote:
> >> Jérôme Pouiller <[email-masked]> writes:
> >> > On Friday 1 October 2021 11:22:08 CEST Kalle Valo wrote:
> >> >> Jerome Pouiller <[email-masked]> writes:
> >> >>
> >> >> > From: Jérôme Pouiller <[email-masked]>
> >> >> >
> >> >> > Signed-off-by: Jérôme Pouiller <[email-masked]>
> >> >>
> >> >> [...]
> >> >>
> >> >> > +/* The device needs data about the antenna configuration. This information in
> >> >> > + * provided by PDS (Platform Data Set, this is the wording used in WF200
> >> >> > + * documentation) files. For hardware integrators, the full process to create
> >> >> > + * PDS files is described here:
> >> >> > + *   https:github.com/SiliconLabs/wfx-firmware/blob/master/PDS/README.md
> >> >> > + *
> >> >> > + * So this function aims to send PDS to the device. However, the PDS file is
> >> >> > + * often bigger than Rx buffers of the chip, so it has to be sent in multiple
> >> >> > + * parts.
> >> >> > + *
> >> >> > + * In add, the PDS data cannot be split anywhere. The PDS files contains tree
> >> >> > + * structures. Braces are used to enter/leave a level of the tree (in a JSON
> >> >> > + * fashion). PDS files can only been split between root nodes.
> >> >> > + */
> >> >> > +int wfx_send_pds(struct wfx_dev *wdev, u8 *buf, size_t len)
> >> >> > +{
> >> >> > +     int ret;
> >> >> > +     int start, brace_level, i;
> >> >> > +
> >> >> > +     start = 0;
> >> >> > +     brace_level = 0;
> >> >> > +     if (buf[0] != '{') {
> >> >> > + dev_err(wdev->dev, "valid PDS start with '{'. Did you forget to
> >> >> > compress it?\n");
> >> >> > +             return -EINVAL;
> >> >> > +     }
> >> >> > +     for (i = 1; i < len - 1; i++) {
> >> >> > +             if (buf[i] == '{')
> >> >> > +                     brace_level++;
> >> >> > +             if (buf[i] == '}')
> >> >> > +                     brace_level--;
> >> >> > +             if (buf[i] == '}' && !brace_level) {
> >> >> > +                     i++;
> >> >> > +                     if (i - start + 1 > WFX_PDS_MAX_SIZE)
> >> >> > +                             return -EFBIG;
> >> >> > +                     buf[start] = '{';
> >> >> > +                     buf[i] = 0;
> >> >> > +                     dev_dbg(wdev->dev, "send PDS '%s}'\n", buf + start);
> >> >> > +                     buf[i] = '}';
> >> >> > +                     ret = hif_configuration(wdev, buf + start,
> >> >> > +                                             i - start + 1);
> >> >> > +                     if (ret > 0) {
> >> >> > + dev_err(wdev->dev, "PDS bytes %d to %d: invalid data (unsupported
> >> >> > options?)\n",
> >> >> > +                                     start, i);
> >> >> > +                             return -EINVAL;
> >> >> > +                     }
> >> >> > +                     if (ret == -ETIMEDOUT) {
> >> >> > + dev_err(wdev->dev, "PDS bytes %d to %d: chip didn't reply (corrupted
> >> >> > file?)\n",
> >> >> > +                                     start, i);
> >> >> > +                             return ret;
> >> >> > +                     }
> >> >> > +                     if (ret) {
> >> >> > + dev_err(wdev->dev, "PDS bytes %d to %d: chip returned an unknown
> >> >> > error\n",
> >> >> > +                                     start, i);
> >> >> > +                             return -EIO;
> >> >> > +                     }
> >> >> > +                     buf[i] = ',';
> >> >> > +                     start = i;
> >> >> > +             }
> >> >> > +     }
> >> >> > +     return 0;
> >> >> > +}
> >> >>
> >> >> 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;
}

-- 
Jérôme Pouiller