Re: [PATCH v3 1/6] cxl/pci: Add RCH downstream port AER and RAS register discovery

Jonathan Cameron
2023-04-13T15:30:59Z

On Tue, 11 Apr 2023 13:02:57 -0500
Terry Bowman <terry.bowman@amd.com> wrote:

> Restricted CXL host (RCH) downstream port AER information is not currently
> logged while in the error state. One problem preventing existing PCIe AER
> functions from logging errors is the AER registers are not accessible. The
> CXL driver requires changes to find RCH downstream port AER registers for
> purpose of error logging.
>
> RCH downstream ports are not enumerated during a PCI bus scan and are
> instead discovered using system firmware, ACPI in this case.[1] The
> downstream port is implemented as a Root Complex Register Block (RCRB).
> The RCRB is a 4k memory block containing PCIe registers based on the PCIe
> root port.[2] The RCRB includes AER extended capability registers used for
> reporting errors. Note, the RCH's AER Capability is located in the RCRB
> memory space instead of PCI configuration space, thus its register access
> is different. Existing kernel PCIe AER functions can not be used to manage
> the downstream port AER capabilities because the port was not enumerated
> during PCI scan and the registers are not PCI config accessible.
>
> Discover RCH downstream port AER extended capability registers. This
> requires using MMIO accesses to search for extended AER capability in
> RCRB register space.
>
> [1] CXL 3.0 Spec, 9.11.2 - System Firmware View of CXL 1.1 Hierarchy
> [2] CXL 3.0 Spec, 8.2.1.1 - RCH Downstream Port RCRB
>
> Co-developed-by: Robert Richter <rrichter@amd.com>
> Signed-off-by: Robert Richter <rrichter@amd.com>
> Signed-off-by: Terry Bowman <terry.bowman@amd.com>

Hi Terry,

Sorry I missed first few versions. Playing catch up.

A few minor comments only inline.

> ---
> drivers/cxl/core/regs.c | 93 +++++++++++++++++++++++++++++++++++------
> drivers/cxl/cxl.h | 5 +++
> drivers/cxl/mem.c | 39 +++++++++++------
> 3 files changed, 113 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/cxl/core/regs.c b/drivers/cxl/core/regs.c
> index 1476a0299c9b..bde1fffab09e 100644
> --- a/drivers/cxl/core/regs.c
> +++ b/drivers/cxl/core/regs.c
> @@ -332,10 +332,36 @@ int cxl_find_regblock(struct pci_dev *pdev, enum cxl_regloc_type type,
> }
> EXPORT_SYMBOL_NS_GPL(cxl_find_regblock, CXL);
>
> +static void __iomem *cxl_map_reg(struct device *dev, struct cxl_register_map *map,
> + char *name)

dev isn't used.

> +{
> +

Trivial but no point in blank line here.

> + if (!request_mem_region(map->resource, map->max_size, name))
> + return NULL;
> +
> + map->base = ioremap(map->resource, map->max_size);
> + if (!map->base) {
> + release_mem_region(map->resource, map->max_size);
> + return NULL;
> + }
> +
> + return map->base;

Why return a value you've already stashed in map->base?

> +}
> +

This is similar enough to devm_cxl_iomap_block() that I'd kind
of like them them take the same parameters. That would mean
moving the map structure outside of the calls and instead passing
in the 3 relevant parameters. Perhaps not worth it.

> +static void cxl_unmap_reg(struct device *dev, struct cxl_register_map *map)
> +{

dev isn't used here either. Makes little sense to pass it in to either funtion.

> + iounmap(map->base);
> + release_mem_region(map->resource, map->max_size);
> +}
> +
> resource_size_t cxl_rcrb_to_component(struct device *dev,
> resource_size_t rcrb,
> enum cxl_rcrb which)
> {
> + struct cxl_register_map map = {
> + .resource = rcrb,
> + .max_size = SZ_4K
> + };
> resource_size_t component_reg_phys;
> void __iomem *addr;
> u32 bar0, bar1;
> @@ -343,7 +369,10 @@ resource_size_t cxl_rcrb_to_component(struct device *dev,
> u32 id;
>
> if (which == CXL_RCRB_UPSTREAM)
> - rcrb += SZ_4K;
> + map.resource += SZ_4K;
> +
> + if (!cxl_map_reg(dev, &map, "CXL RCRB"))
> + return CXL_RESOURCE_NONE;
>
> /*
> * RCRB's BAR[0..1] point to component block containing CXL
> @@ -351,21 +380,12 @@ resource_size_t cxl_rcrb_to_component(struct device *dev,
> * the PCI Base spec here, esp. 64 bit extraction and memory
> * ranges alignment (6.0, 7.5.1.2.1).
> */
> - if (!request_mem_region(rcrb, SZ_4K, "CXL RCRB"))
> - return CXL_RESOURCE_NONE;
> - addr = ioremap(rcrb, SZ_4K);
> - if (!addr) {
> - dev_err(dev, "Failed to map region %pr\n", addr);
> - release_mem_region(rcrb, SZ_4K);
> - return CXL_RESOURCE_NONE;
> - }
> -
> + addr = map.base;

I'd have preferred to see this refactor as a precursor patch to the
'real changes' that follow.

> id = readl(addr + PCI_VENDOR_ID);
> cmd = readw(addr + PCI_COMMAND);
> bar0 = readl(addr + PCI_BASE_ADDRESS_0);
> bar1 = readl(addr + PCI_BASE_ADDRESS_1);
> - iounmap(addr);
> - release_mem_region(rcrb, SZ_4K);
> + cxl_unmap_reg(dev, &map);
>
> /*
> * Sanity check, see CXL 3.0 Figure 9-8 CXL Device that Does Not
> @@ -396,3 +416,52 @@ resource_size_t cxl_rcrb_to_component(struct device *dev,
> return component_reg_phys;
> }
> EXPORT_SYMBOL_NS_GPL(cxl_rcrb_to_component, CXL);

...

> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 044a92d9813e..df64c402e6e6 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -270,6 +270,9 @@ enum cxl_rcrb {
> resource_size_t cxl_rcrb_to_component(struct device *dev,
> resource_size_t rcrb,
> enum cxl_rcrb which);
> +u16 cxl_rcrb_to_aer(struct device *dev, resource_size_t rcrb);
> +u16 cxl_component_to_ras(struct device *dev,
> + resource_size_t component_reg_phys);
>
> #define CXL_RESOURCE_NONE ((resource_size_t) -1)
> #define CXL_TARGET_STRLEN 20
> @@ -601,6 +604,8 @@ struct cxl_dport {
> int port_id;
> resource_size_t component_reg_phys;
> resource_size_t rcrb;
> + u16 aer_cap;
> + u16 ras_cap;

This structure has kernel-doc that needs to be updated for these new entries.

> bool rch;
> struct cxl_port *port;
> };
> diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> index 39c4b54f0715..014295ab6bc6 100644
> --- a/drivers/cxl/mem.c
> +++ b/drivers/cxl/mem.c
> @@ -45,13 +45,36 @@ static int cxl_mem_dpa_show(struct seq_file *file, void *data)
> return 0;
> }
>
> +static void cxl_setup_rcrb(struct cxl_dev_state *cxlds,
> + struct cxl_dport *parent_dport)
> +{
> + struct cxl_memdev *cxlmd = cxlds->cxlmd;

extra space before =

> +
> + if (!parent_dport->rch)
> + return;
> +
> + /*
> + * The component registers for an RCD might come from the
> + * host-bridge RCRB if they are not already mapped via the
> + * typical register locator mechanism.
> + */
> + if (cxlds->component_reg_phys == CXL_RESOURCE_NONE)
> + cxlds->component_reg_phys = cxl_rcrb_to_component(
> + &cxlmd->dev, parent_dport->rcrb, CXL_RCRB_UPSTREAM);
> +
> + parent_dport->aer_cap = cxl_rcrb_to_aer(parent_dport->dport,
> + parent_dport->rcrb);
> +
> + parent_dport->ras_cap = cxl_component_to_ras(parent_dport->dport,
> + parent_dport->component_reg_phys);
> +}
> +
> static int devm_cxl_add_endpoint(struct device *host, struct cxl_memdev *cxlmd,
> struct cxl_dport *parent_dport)
> {
> struct cxl_port *parent_port = parent_dport->port;
> struct cxl_dev_state *cxlds = cxlmd->cxlds;
> struct cxl_port *endpoint, *iter, *down;
> - resource_size_t component_reg_phys;
> int rc;
>
> /*
> @@ -66,17 +89,9 @@ static int devm_cxl_add_endpoint(struct device *host, struct cxl_memdev *cxlmd,
> ep->next = down;
> }
>
> - /*
> - * The component registers for an RCD might come from the
> - * host-bridge RCRB if they are not already mapped via the
> - * typical register locator mechanism.
> - */
> - if (parent_dport->rch && cxlds->component_reg_phys == CXL_RESOURCE_NONE)
> - component_reg_phys = cxl_rcrb_to_component(
> - &cxlmd->dev, parent_dport->rcrb, CXL_RCRB_UPSTREAM);
> - else
> - component_reg_phys = cxlds->component_reg_phys;
> - endpoint = devm_cxl_add_port(host, &cxlmd->dev, component_reg_phys,
> + cxl_setup_rcrb(cxlds, parent_dport);
> +
> + endpoint = devm_cxl_add_port(host, &cxlmd->dev, cxlds->component_reg_phys,
> parent_dport);
As above, I'd prefer to see this refactor done in a precursor patch before the new
stuff is added. I like reviewing noop patches as I don't have to think much (so
can do it when I'm supposedly in a meeting ;)

Jonathan
> if (IS_ERR(endpoint))
> return PTR_ERR(endpoint);