[PATCH v4 1/8] swiotlb: make io_tlb_default_mem local to swiotlb.c
Petr Tesařík
petr at tesarici.cz
Thu Jul 20 00:54:10 PDT 2023
On Thu, 20 Jul 2023 08:37:44 +0200
Christoph Hellwig <hch at lst.de> wrote:
> On Thu, Jul 13, 2023 at 05:23:12PM +0200, Petr Tesarik wrote:
> > From: Petr Tesarik <petr.tesarik.ext at huawei.com>
> >
> > SWIOTLB implementation details should not be exposed to the rest of the
> > kernel. This will allow to make changes to the implementation without
> > modifying non-swiotlb code.
> >
> > To avoid breaking existing users, provide helper functions for the few
> > required fields.
> >
> > As a bonus, using a helper function to initialize struct device allows to
> > get rid of an #ifdef in driver core.
> >
> > Signed-off-by: Petr Tesarik <petr.tesarik.ext at huawei.com>
> > ---
> > arch/arm/xen/mm.c | 2 +-
> > arch/mips/pci/pci-octeon.c | 2 +-
> > arch/x86/kernel/pci-dma.c | 2 +-
> > drivers/base/core.c | 4 +---
> > drivers/xen/swiotlb-xen.c | 2 +-
> > include/linux/swiotlb.h | 25 +++++++++++++++++++++++-
> > kernel/dma/swiotlb.c | 39 +++++++++++++++++++++++++++++++++++++-
> > 7 files changed, 67 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> > index 3d826c0b5fee..0f32c14eb786 100644
> > --- a/arch/arm/xen/mm.c
> > +++ b/arch/arm/xen/mm.c
> > @@ -125,7 +125,7 @@ static int __init xen_mm_init(void)
> > return 0;
> >
> > /* we can work with the default swiotlb */
> > - if (!io_tlb_default_mem.nslabs) {
> > + if (!is_swiotlb_allocated()) {
> > rc = swiotlb_init_late(swiotlb_size_or_default(),
> > xen_swiotlb_gfp(), NULL);
> > if (rc < 0)
>
> I'd much rather move the already initialized check into
> swiotlb_init_late, which is a much cleaer interface.
>
> > /* we can work with the default swiotlb */
> > - if (!io_tlb_default_mem.nslabs) {
> > + if (!is_swiotlb_allocated()) {
> > int rc = swiotlb_init_late(swiotlb_size_or_default(),
> > GFP_KERNEL, xen_swiotlb_fixup);
> > if (rc < 0)
>
> .. and would take care of this one as well.
Oh, you're right! These are the only two places that look at
io_tlb_default_mem.nslabs, and all they need is to avoid double
initialization. Makes perfect sense to move it inside
swiotlb_init_late().
> > +bool is_swiotlb_allocated(void)
> > +{
> > + return !!io_tlb_default_mem.nslabs;
>
> Nit: no need for the !!, we can rely on the implicit promotion to
> bool. But with the suggestion above the need for this helper
> should go away anyway.
Eh, yes. I initially declared the return type as int and then forgot to
change the return statement. But as you say, the whole function will go
away entirely.
Petr T
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