linux-kernel - Re: [PATCH v2 06/12] cxl/acpi: Extract component registers of restricted hosts from RCRB

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Date:   Mon, 24 Oct 2022 14:24:54 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Robert Richter <rrichter@....com>,
        Dan Williams <dan.j.williams@...el.com>
CC:     Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        "Jonathan Cameron" <Jonathan.Cameron@...wei.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Terry Bowman <terry.bowman@....com>
Subject: Re: [PATCH v2 06/12] cxl/acpi: Extract component registers of
 restricted hosts from RCRB

Robert Richter wrote:
> On 20.10.22 22:17:07, Dan Williams wrote:
> > Robert Richter wrote:
> > > A downstream port must be connected to a component register block.
> > > For restricted hosts the base address is determined from the RCRB. The
> > > RCRB is provided by the host's CEDT CHBS entry. Rework CEDT parser to
> > > get the RCRB and add code to extract the component register block from
> > > it.
> > > 
> > > RCRB's BAR[0..1] point to the component block containing CXL subsystem
> > > component registers. MEMBAR extraction follows the PCI base spec here,
> > > esp. 64 bit extraction and memory range alignment (6.0, 7.5.1.2.1).
> > > 
> > > Note: Right now the component register block is used for HDM decoder
> > > capability only which is optional for RCDs. If unsupported by the RCD,
> > > the HDM init will fail. It is future work to bypass it in this case.
> > > 
> > > Signed-off-by: Terry Bowman <terry.bowman@....com>
> > > Signed-off-by: Robert Richter <rrichter@....com>
> > > ---
> > >  drivers/cxl/acpi.c | 79 ++++++++++++++++++++++++++++++++++++++++------
> > >  1 file changed, 69 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> > > index fb9f72813067..a92d5d7b7a92 100644
> > > --- a/drivers/cxl/acpi.c
> > > +++ b/drivers/cxl/acpi.c
> > > @@ -9,6 +9,8 @@
> > >  #include "cxlpci.h"
> > >  #include "cxl.h"
> > >  
> > > +#define CXL_RCRB_SIZE	SZ_8K
> > > +
> > >  static unsigned long cfmws_to_decoder_flags(int restrictions)
> > >  {
> > >  	unsigned long flags = CXL_DECODER_F_ENABLE;
> > > @@ -229,27 +231,82 @@ static int add_host_bridge_uport(struct device *match, void *arg)
> > >  struct cxl_chbs_context {
> > >  	struct device *dev;
> > >  	unsigned long long uid;
> > > -	resource_size_t chbcr;
> > > +	struct acpi_cedt_chbs chbs;
> > >  };
> > >  
> > > -static int cxl_get_chbcr(union acpi_subtable_headers *header, void *arg,
> > > -			 const unsigned long end)
> > > +static int cxl_get_chbs(union acpi_subtable_headers *header, void *arg,
> > > +			const unsigned long end)
> > >  {
> > >  	struct cxl_chbs_context *ctx = arg;
> > >  	struct acpi_cedt_chbs *chbs;
> > >  
> > > -	if (ctx->chbcr)
> > > +	if (ctx->chbs.base)
> > >  		return 0;
> > >  
> > >  	chbs = (struct acpi_cedt_chbs *) header;
> > >  
> > >  	if (ctx->uid != chbs->uid)
> > >  		return 0;
> > > -	ctx->chbcr = chbs->base;
> > > +	ctx->chbs = *chbs;
> > >  
> > >  	return 0;
> > >  }
> > >  
> > > +static resource_size_t cxl_get_chbcr(struct cxl_chbs_context *ctx)
> > > +{
> > 
> > The core logic of this looks good, but this wants to be shared with the
> > upstream port component register discovery.
> > 
> > Full disclosure I am reconciling these patches with an attempt that Dave
> > Jiang made at this topic. Since your series hit the list first I will
> > let it take the lead, but then fill it in with comments and learnings
> > from Dave's effort.
> > 
> > So in this case Dave moved this into the drivers/cxl/core/regs.c with a
> > function signature like:
> > 
> > enum cxl_rcrb {
> >        CXL_RCRB_DOWNSTREAM,
> >        CXL_RCRB_UPSTREAM,
> > };
> > 
> > resource_size_t cxl_rcrb_to_component(struct device *dev,
> >                                       resource_size_t rcrb_base, int len,
> >                                       enum cxl_rcrb which);
> > 
> > ...where @which alternates when called by cxl_acpi for the downstream
> > case, or cxl_mem for the upstream case.
> 
> Ok, I see where to go here. Could you point me to Dave's postings you
> are referring to? I checked linux-cxl and could not find anything
> related to RCRB or that changes regs.c.

He was in the middle of tidying them when you posted your series, but I
think it would not hurt to push them to a git tree so you can grab the
bits and pieces you want.

Dave?