RE: [PATCH 2/3] iommu/ipmmu-vmsa: Calculate context registers' offset instead of a macro

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>]

Hi Geert-san,

> From: Geert Uytterhoeven, Sent: Friday, October 11, 2019 9:29 PM
> 
> Hi Shimoda-san,
> 
> On Wed, Oct 9, 2019 at 10:27 AM Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@renesas.com> wrote:
> > Since we will have changed memory mapping of the IPMMU in the future,
> > this patch uses ipmmu_features values instead of a macro to
> > calculate context registers offset. No behavior change.
> >
> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> 
> Thanks for your patch!
> 
> > --- a/drivers/iommu/ipmmu-vmsa.c
> > +++ b/drivers/iommu/ipmmu-vmsa.c
> > @@ -50,6 +50,8 @@ struct ipmmu_features {
> >         bool twobit_imttbcr_sl0;
> >         bool reserved_context;
> >         bool cache_snoop;
> > +       u32 ctx_offset_base;
> > +       u32 ctx_offset_stride;
> >  };
> >
> >  struct ipmmu_vmsa_device {
> > @@ -99,8 +101,6 @@ static struct ipmmu_vmsa_device *to_ipmmu(struct device *dev)
> >
> >  #define IM_NS_ALIAS_OFFSET             0x800
> >
> > -#define IM_CTX_SIZE                    0x40
> > -
> >  #define IMCTR                          0x0000
> >  #define IMCTR_TRE                      (1 << 17)
> >  #define IMCTR_AFE                      (1 << 16)
> > @@ -253,18 +253,25 @@ static void ipmmu_write(struct ipmmu_vmsa_device *mmu, unsigned int offset,
> >         iowrite32(data, mmu->base + offset);
> >  }
> >
> > +static u32 ipmmu_ctx_reg(struct ipmmu_vmsa_device *mmu, unsigned int context_id,
> > +                        unsigned int reg)
> > +{
> > +       return mmu->features->ctx_offset_base +
> > +              context_id * mmu->features->ctx_offset_stride + reg;
> > +}
> > +
> >  static u32 ipmmu_ctx_read_root(struct ipmmu_vmsa_domain *domain,
> >                                unsigned int reg)
> >  {
> >         return ipmmu_read(domain->mmu->root,
> > -                         domain->context_id * IM_CTX_SIZE + reg);
> > +                         ipmmu_ctx_reg(domain->mmu, domain->context_id, reg));
> 
> For consistency:
> 
>     ipmmu_ctx_reg(domain->mmu->root, ...)
> 
> but in practice the features for domain->mmu and domain->mmu->root are
> identical anyway.
> 
> >  }
> >
> >  static void ipmmu_ctx_write_root(struct ipmmu_vmsa_domain *domain,
> >                                  unsigned int reg, u32 data)
> >  {
> >         ipmmu_write(domain->mmu->root,
> > -                   domain->context_id * IM_CTX_SIZE + reg, data);
> > +                   ipmmu_ctx_reg(domain->mmu, domain->context_id, reg), data);
> 
> Likewise:
> 
>     ipmmu_ctx_reg(domain->mmu->root, ...)?

Thank you for the comments! Yes, we can use domain->mmu->root to ipmmu_ctx_reg()
because ipmmu_ctx_reg() only use mmu->features.

> I find these ipmmu_{read,write}() a bit hard too read, with passing the
> mmu to both ipmmu_{read,write}() and ipmmu_ctx_reg().

I completely agree.

> What do you think about providing two helpers ipmmu_ctx_{read,write}(),
> so all users can just use e.g.
> 
>     ipmmu_ctx_write(mmu, context_id, reg, data);
> 
> instead of
> 
>     ipmmu_write(mmu, ipmmu_ctx_reg(mmu, context_id, reg), data);
> 
> ?

I think so. I'll fix it. Perhaps, I'll make a patch which changes
the function name at first.

Best regards,
Yoshihiro Shimoda

> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds