Message-ID: <1948585.sCnHgVVQio@pc-42>
Date:   Wed, 10 Nov 2021 12:10:16 +0100
From:   Jérôme Pouiller <jerome.pouiller@...abs.com>
To:     Kalle Valo <kvalo@...eaurora.org>
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

On Wednesday 10 November 2021 10:58:41 CET Kalle Valo wrote:
> Jérôme Pouiller <jerome.pouiller@...abs.com> writes:
> > On Thursday 7 October 2021 12:49:47 CEST Kalle Valo wrote:
> >> Kalle Valo <kvalo@...eaurora.org> writes:
> >> > 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.
> >>
> >> Sorry, I read this too hastily. I just saw "buf[start] != '{'" and
> >> assumed this is the same ASCII format, but not sure anymore. Can you
> >> explain what changes you made now?
> >
> > The script I am going to write will compute where the PDS have to be split
> > (this work is currently done by the driver). The script will add a
> > separating character (let's say '\0') between each chunk.
> >
> > The driver will just have to find the separating character, send the
> > chunk and repeat.
> 
> I would forget ASCII altogether and implement a proper binary format
> like TLV. For example, ath10k uses TLV with board-2.bin files (grep for
> enum ath10k_bd_ie_type).

Maybe you plan to have common functions to parse TLV files? Without that,
I do not see so much benefits to TLV. However, it does not cost me so
much. So all right, I'll do.

> Also I recommend changing the file "signature" ('{') to something else
> so that the driver detects incorrect formats. And maybe even use suffix
> .pds2 or something like that to make it more obvious and avoid
> confusion?

Maybe I could replace '{' by '\x7b'? :)

More seriously, this value is enforced by the device. However, with the
introduction of TLV, I will already test the value of the Type field, so
I think this test will be less important and I could remove it.


-- 
Jérôme Pouiller

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