Re: [PATCH 4/4] spi: dw: Add Synopsys Component version reading and parsing

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Sat, Nov 13, 2021 at 2:19 AM Serge Semin <fancer.lancer@xxxxxxxxx> wrote:
> On Sat, Nov 13, 2021 at 01:14:30AM +0200, Andy Shevchenko wrote:
> > On Saturday, November 13, 2021, Serge Semin <fancer.lancer@xxxxxxxxx> wrote:
> > > On Fri, Nov 12, 2021 at 11:37:36PM +0200, Andy Shevchenko wrote:
> > > > On Fri, Nov 12, 2021 at 11:27 PM Andy Shevchenko
> > > > <andy.shevchenko@xxxxxxxxx> wrote:
> > > > > On Fri, Nov 12, 2021 at 10:52 PM Serge Semin
> > > > > <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> wrote:

...

> > > > > > +       /*
> > > > > > +        * Retrieve the Synopsys component version if it hasn't been
> > > specified
> > > > > > +        * by the platform. Note the CoreKit version ID is encoded
> > > as a 4bytes
> > > > > > +        * ASCII string enclosed with '*' symbol.
> > > > > > +        */
> > > > > > +       if (!dws->ver) {
> > > > > > +               u32 comp;
> > > > > > +
> > > > > > +               comp = dw_readl(dws, DW_SPI_VERSION);
> > > > > > +               dws->ver = (DW_SPI_GET_BYTE(comp, 3) - '0') * 100;
> > > > > > +               dws->ver += (DW_SPI_GET_BYTE(comp, 2) - '0') * 10;
> > > > > > +               dws->ver += (DW_SPI_GET_BYTE(comp, 1) - '0');
> > > > > > +
> > > > > > +               dev_dbg(dev, "Synopsys DWC%sSSI v%u.%02u\n",
> > > > > > +                       (dws->caps & DW_SPI_CAP_DWC_HSSI) ? " " : "
> > > APB ",
> > > > > > +                       dws->ver / 100, dws->ver % 100);
> > > > >
> > >
> > > > > Oh lą lą, first you multiply then you divide in the same piece of code!
> > > > > What's wrong with fourcc (and thus keep it in ver filed as is) ? (Also
> > > > > we have %p4cc)
> > >
> > > Please note that's just a dev_DBG() print. So division has been used
> > > in there to check whether the conversion was correct. The whole idea
> > > behind the code above it was to retrieve the Component version as a
> > > single number so then it could be used by the driver code in a simple
> > > statement with a normal integer operation. For instance in case if we
> > > need to check whether DW SSI IP-core version is greater than 1.01 we'd
> > > have something like this: if (dws->ver > 101). Here 101 looks at least
> > > close to the original 1.01. How would the statement look with four
> > > chars? Of course we could add an another macro which would look like
> > > this:
> > > #define DW_SSI_VER(_maj, _mid, _min) \
> > >         ((_maj) << 24 | (_mid) << 16 | (_min) << 8 | '*')
> > > and use it with raw version ID, like this
> > > (dws->ver > DW_SSI_VER('1', '0', '1')). But IMO it doesn't look
> > > better if not worse.
> > > Alternatively we could split the version ID into two parts with
> > > major and minor numbers. But normally one doesn't make much sense
> > > without another so each statement would need to check both of them
> > > at once anyway. So I decided to stick with a simplest solution and
> > > combined them into a single storage. Have you got a better idea of
> > > how to implement this functionality?
>
> > Then check DWC3 driver which relies on IZp version a lot.
>
> I'm still not convinced that the DWC3 solution would be better in this case.
> (I had a similar approach in mind though.) Although it might be suitable
> here seeing we could take the IP generation into account in a single
> macro. But at the same time having macros defined for each version may
> eventually turn into a clumsy set of macros space as it happened in DWC3.
>
> I don't understand what do you see wrong in the suggested here
> solution except a math in the debug string?

The transformation ruins the fourcc [1] representation. We know that
this is an ASCII. We know the position and meaning of each from 4
characters.

[1]: https://en.wikipedia.org/wiki/FourCC

> Why would you prefer the
> DWC3 approach better than the one implemented in my patch?

You asked what is _better_ implementation than yours. It doesn't mean
the DWC3 approach fully fits here, but
- SPI DW has the same issue as DWC3 solves, i.e. different version
lines for two or more IPs of the same kind (see DWC3, DWC31, DWC32)
- it doesn't ruins 4cc

In case if we need to print it, I would rather see something in %p4cc
implementation than customized 100500 approaches spreaded over the
entire kernel.

> I don't really see much benefits in it:
> if (dws->ver > 101)
> or
> if (DW_SPI_VER_AFTER(dws, 101))
> In both cases version ID isn't represented in the original
> Vendor-defined structure, like "1.01". The only part which could be
> considered as better in DWC3 approach is having a macro name, which gives
> a bit better notion about the operation. But does it really worth
> introducing a new abstraction in the driver?
>
> On the other hand we could intermix the approaches. For instance decode
> the Component version as I suggested in this patch and implement a set of
> version checking macro. Thus we won't need so many additional macro
> encoding the SSI_COMP_VERSION content.
>
> If only we could have a macro like DW_SPI_VER(dws, >=, "1.01a") with no
> performance drawbacks I'd be glad to use it. AFAIU compiler can't
> operate with the string literal symbols, thus the symbols extraction
> like "1.01a"[0] will be performed on each statement execution which isn't
> that performant comparing to a simple two integers comparison.
>
> BTW note the DWC3 macros implicitly depend on having a local variable
> with dwc name which violates the kernel coding style.

> > > > > > +       }
> > >
> > > > Have you seen this, btw?
> > > >
> > > > https://elixir.bootlin.com/linux/latest/source/drivers/
> > > tty/serial/8250/8250_dwlib.c#L93
> > >
> > > It doesn't utilized version ID for something functional, but just
> > > prints it to the console. So it isn't that good reference in this
> > > case.

Depends what you would like to do with this. If it's only for
information to the developer, then it fits, if you need to compare,
then see above.

-- 
With Best Regards,
Andy Shevchenko