Re: [PATCH 1/2] hw/cxl: Add utility functions decoder interleave ways and target count.

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Mon, 4 Sep 2023 20:26:59 +0200
Philippe Mathieu-Daudé <philmd@linaro.org> wrote:

> On 4/9/23 18:47, Jonathan Cameron wrote:
> > As an encoded version of these key configuration parameters is
> > a register, provide functions to extract it again so as to avoid
> > the need for duplicating the storage.
> > 
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > ---
> >   include/hw/cxl/cxl_component.h | 14 ++++++++++++++
> >   hw/cxl/cxl-component-utils.c   | 17 +++++++++++++++++
> >   2 files changed, 31 insertions(+)
> > 
> > diff --git a/include/hw/cxl/cxl_component.h b/include/hw/cxl/cxl_component.h
> > index 42c7e581a7..f0ad9cf7de 100644
> > --- a/include/hw/cxl/cxl_component.h
> > +++ b/include/hw/cxl/cxl_component.h
> > @@ -238,7 +238,21 @@ static inline int cxl_decoder_count_enc(int count)
> >       return 0;
> >   }
> >   
> > +static inline int cxl_decoder_count_dec(int enc_cnt)
> > +{
> > +    switch (enc_cnt) {
> > +    case 0: return 1;
> > +    case 1: return 2;
> > +    case 2: return 4;
> > +    case 3: return 6;
> > +    case 4: return 8;
> > +    case 5: return 10;
> > +    }
> > +    return 0;
> > +}  
> 
> Why inline?
> 

Bad habit.


> Alternatively:
> 
>    unsigned cxl_decoder_count_dec(unsigned enc_cnt)
>    {
>        return enc_cnt <= 5 ? 2 * enc_cnt : 0;

It gets a little more fiddly than the code I'm proposing implies.
For Switches and Host Bridges larger values are defined
(we just don't emulate them yet and may never do so) and those
don't have a sensible mapping. 

I guess there is no harm in adding the full decode however
which will make it more obvious why it was a switch statement.

>    }
> 
>