> -----Original Message-----
> From: Alex Williamson <[email protected]>
> Sent: Wednesday, August 26, 2026 2:56 AM
> To: Manish Honap <[email protected]>
> Cc: [email protected]; Ankit Agrawal <[email protected]>; [email protected];
> [email protected]; [email protected]; Srirangan Madhavan
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; Yishai Hadas
> <[email protected]>; Shameer Kolothum Thodi
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]; Neo Jia
> <[email protected]>; Krishnakant Jaju <[email protected]>; Vikram Sethi
> <[email protected]>; Zhi Wang <[email protected]>; linux-
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; linux-
> [email protected]; [email protected]; [email protected]
> Subject: Re: [PATCH v4 02/27] cxl/regs: Skip sub-block region request for BAR-
> owning drivers
>
> External email: Use caution opening links or attachments
>
>
> On Thu, 13 Aug 2026 15:06:06 +0530
> <[email protected]> wrote:
>
> > From: Manish Honap <[email protected]>
> >
> > cxl_map_component_regs() claims each mapped sub-block with
> > devm_request_mem_region(). A driver that owns the whole component
> > register BAR, such as vfio-cxl, has already claimed the full BAR, so
> > the per-sub-block claim collides and the mapping fails.
> >
> > Add a bar_owned parameter to cxl_pci_setup_regs() and record it in
> > skip_sub_bar_request on the register map. When set, cxl-core maps the
> > sub-block without requesting the region and leaves ownership with the
> > upper driver. cxl_pci passes false and keeps its existing claim,
> > preserving /dev/mem tooling access to the rest of the component space.
>
> The bool arg itself is an undesirable shape, but then threading it through
> @bar_owned to @skip_sub_bar_request to @request is difficult to follow with
> limited utility.
>
> What if instead cxl allowed drivers to register the resources they've already
> requested into the reg_map, ex:
>
> int cxl_reg_map_add_owned_resource(struct cxl_register_map *reg_map,
> struct resource *res)
>
> Then before cxl does any devm_request_mem_region() calls it creates a
> temporary struct resource for the range it wants to request and compares it to
> the resources the driver already reported as owned via resource_contains()?
>
> I'm picking reg_map vs cxlds because it seems easier to thread through to
> where we need it. In this flow, devm_cxl_iomap_block() could be split into
> devm_cxl_request_block() and devm_cxl_ioremap_block(), where
> cxl_map_component_regs() would conditionally call the former when
> resource_contains() finds no matches for driver owned resources, and the
> latter is called unconditionally. devm_cxl_iomap_block() could remain as the
> unconditional user of both. Thanks,
>
> Alex
Thanks, agreed on both counts; I will switch to the registered-resource
cxl_reg_map_add_owned_resource approach you described.
Manish
