Re: [PATCH v15 06/16] cxl: Move HDM decoder helpers to built-in code

[Dave Jiang]

On 10/10/26 7:14 PM, Srirangan Madhavan wrote:
> The PCI core will restore HDM decoders after a reset, possibly while no
> CXL driver is loaded, so it cannot call into cxl_core.
> 
> Move the HDM register programming helpers from hdm.c to hdm_regs.c and
> build that file into the kernel whenever CXL_BUS is enabled, including
> when CXL_BUS is modular. Export only the symbols that cxl_core uses.
> 
> Keep the DPA lock assertion in the normal decoder programming caller so
> the register helpers do not depend on cxl_rwsem. Leave cxl_rwsem in
> cxl_core until built-in cache management needs it.
> 
> Link: https://git.kernel.org/pub/scm/linux/kernel/git/djiang/linux.git/commit/?id=e0b476ea99567fb5aa416eac0cf61bca20724880
> Suggested-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> Signed-off-by: Srirangan Madhavan <smadhavan@xxxxxxxxxx>

Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>

> ---
>  drivers/cxl/core/Makefile   |   1 +
>  drivers/cxl/core/hdm.c      | 102 +------------------------------
>  drivers/cxl/core/hdm_regs.c | 118 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 121 insertions(+), 100 deletions(-)
>  create mode 100644 drivers/cxl/core/hdm_regs.c
> 
> diff --git a/drivers/cxl/core/Makefile b/drivers/cxl/core/Makefile
> index ce7213818d3c..6703c1729396 100644
> --- a/drivers/cxl/core/Makefile
> +++ b/drivers/cxl/core/Makefile
> @@ -1,5 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_CXL_BUS) += cxl_core.o
> +obj-$(subst m,y,$(CONFIG_CXL_BUS)) += hdm_regs.o
>  obj-$(CONFIG_CXL_SUSPEND) += suspend.o
>  
>  ccflags-y += -I$(srctree)/drivers/cxl
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 7d3254a712e4..47cf49bcd2e5 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -708,35 +708,6 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, u64 size)
>  	return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
>  }
>  
> -static void cxld_set_interleave(const struct cxl_decoder_config *config, u32 *ctrl)
> -{
> -	u16 eig;
> -	u8 eiw;
> -
> -	/*
> -	 * Input validation ensures these warns never fire, but otherwise
> -	 * suppress unititalized variable usage warnings.
> -	 */
> -	if (WARN_ONCE(ways_to_eiw(config->interleave_ways, &eiw),
> -		      "invalid interleave_ways: %d\n", config->interleave_ways))
> -		return;
> -	if (WARN_ONCE(granularity_to_eig(config->interleave_granularity, &eig),
> -		      "invalid interleave_granularity: %d\n",
> -		      config->interleave_granularity))
> -		return;
> -
> -	u32p_replace_bits(ctrl, eig, CXL_HDM_DECODER0_CTRL_IG_MASK);
> -	u32p_replace_bits(ctrl, eiw, CXL_HDM_DECODER0_CTRL_IW_MASK);
> -	*ctrl |= CXL_HDM_DECODER0_CTRL_COMMIT;
> -}
> -
> -static void cxld_set_type(const struct cxl_decoder_config *config, u32 *ctrl)
> -{
> -	u32p_replace_bits(ctrl,
> -			  !!(config->target_type == CXL_DECODER_HOSTONLYMEM),
> -			  CXL_HDM_DECODER0_CTRL_HOSTONLY);
> -}
> -
>  static void cxlsd_set_targets(struct cxl_switch_decoder *cxlsd, u64 *tgt)
>  {
>  	struct cxl_dport **t = &cxlsd->target[0];
> @@ -759,77 +730,6 @@ static void cxlsd_set_targets(struct cxl_switch_decoder *cxlsd, u64 *tgt)
>  		*tgt |= FIELD_PREP(GENMASK_ULL(63, 56), t[7]->port_id);
>  }
>  
> -/*
> - * Per CXL 2.0 8.2.5.12.20 Committing Decoder Programming, hardware must set
> - * committed or error within 10ms, but just be generous with 20ms to account for
> - * clock skew and other marginal behavior
> - */
> -#define COMMIT_TIMEOUT_MS 20
> -int cxld_await_commit(void __iomem *hdm, int id)
> -{
> -	u32 ctrl;
> -	int i;
> -
> -	for (i = 0; i < COMMIT_TIMEOUT_MS; i++) {
> -		ctrl = readl(hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> -		if (FIELD_GET(CXL_HDM_DECODER0_CTRL_COMMIT_ERROR, ctrl)) {
> -			ctrl &= ~CXL_HDM_DECODER0_CTRL_COMMIT;
> -			writel(ctrl, hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> -			return -EIO;
> -		}
> -		if (FIELD_GET(CXL_HDM_DECODER0_CTRL_COMMITTED, ctrl))
> -			return 0;
> -		fsleep(1000);
> -	}
> -
> -	return -ETIMEDOUT;
> -}
> -
> -static u32 cxl_hdm_write_range(void __iomem *hdm,
> -			       const struct cxl_decoder_config *config)
> -{
> -	u64 size = range_len(&config->hpa_range);
> -	u64 base = config->hpa_range.start;
> -	int id = config->id;
> -	u32 ctrl;
> -
> -	ctrl = readl(hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> -	cxld_set_interleave(config, &ctrl);
> -	cxld_set_type(config, &ctrl);
> -
> -	writel(upper_32_bits(base), hdm + CXL_HDM_DECODER0_BASE_HIGH_OFFSET(id));
> -	writel(lower_32_bits(base), hdm + CXL_HDM_DECODER0_BASE_LOW_OFFSET(id));
> -	writel(upper_32_bits(size), hdm + CXL_HDM_DECODER0_SIZE_HIGH_OFFSET(id));
> -	writel(lower_32_bits(size), hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(id));
> -	return ctrl;
> -}
> -
> -void cxl_commit_start_endpoint(const struct cxl_endpoint_decoder_settings *settings,
> -			       void __iomem *hdm)
> -{
> -	int id = settings->config.id;
> -	u32 ctrl;
> -
> -	lockdep_assert_held(&cxl_rwsem.dpa);
> -	ctrl = cxl_hdm_write_range(hdm, &settings->config);
> -	writel(upper_32_bits(settings->skip), hdm + CXL_HDM_DECODER0_SKIP_HIGH(id));
> -	writel(lower_32_bits(settings->skip), hdm + CXL_HDM_DECODER0_SKIP_LOW(id));
> -	writel(ctrl, hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> -}
> -
> -void cxl_commit_start_switch(const struct cxl_decoder_config *config,
> -			     u64 targets, void __iomem *hdm)
> -{
> -	int id = config->id;
> -	u32 ctrl;
> -
> -	lockdep_assert_held(&cxl_rwsem.dpa);
> -	ctrl = cxl_hdm_write_range(hdm, config);
> -	writel(upper_32_bits(targets), hdm + CXL_HDM_DECODER0_TL_HIGH(id));
> -	writel(lower_32_bits(targets), hdm + CXL_HDM_DECODER0_TL_LOW(id));
> -	writel(ctrl, hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> -}
> -
>  static void
>  cxl_endpoint_decoder_snapshot(struct cxl_endpoint_decoder *cxled,
>  			      struct cxl_endpoint_decoder_settings *settings)
> @@ -846,6 +746,8 @@ static void setup_hw_decoder(struct cxl_decoder *cxld, void __iomem *hdm)
>  {
>  	struct cxl_endpoint_decoder_settings settings;
>  
> +	lockdep_assert_held(&cxl_rwsem.dpa);
> +
>  	if (is_switch_decoder(&cxld->dev)) {
>  		struct cxl_switch_decoder *cxlsd =
>  			to_cxl_switch_decoder(&cxld->dev);
> diff --git a/drivers/cxl/core/hdm_regs.c b/drivers/cxl/core/hdm_regs.c
> new file mode 100644
> index 000000000000..53d2f236e49c
> --- /dev/null
> +++ b/drivers/cxl/core/hdm_regs.c
> @@ -0,0 +1,118 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright (c) 2026 NVIDIA Corporation & Affiliates */
> +#include <linux/delay.h>
> +#include <linux/bug.h>
> +#include <linux/errno.h>
> +#include <linux/export.h>
> +#include <linux/kernel.h>
> +
> +#include <cxl/hdm.h>
> +
> +#include "cxl.h"
> +#include "core.h"
> +
> +/*
> + * HDM decoder register helpers are built in whenever CXL_BUS is enabled,
> + * including when cxl_core is modular. Callers provide any required locking.
> + */
> +
> +static void cxld_set_interleave(const struct cxl_decoder_config *config, u32 *ctrl)
> +{
> +	u16 eig;
> +	u8 eiw;
> +
> +	/*
> +	 * Input validation ensures these warns never fire, but otherwise
> +	 * suppress unititalized variable usage warnings.
> +	 */
> +	if (WARN_ONCE(ways_to_eiw(config->interleave_ways, &eiw),
> +		      "invalid interleave_ways: %d\n", config->interleave_ways))
> +		return;
> +	if (WARN_ONCE(granularity_to_eig(config->interleave_granularity, &eig),
> +		      "invalid interleave_granularity: %d\n",
> +		      config->interleave_granularity))
> +		return;
> +
> +	u32p_replace_bits(ctrl, eig, CXL_HDM_DECODER0_CTRL_IG_MASK);
> +	u32p_replace_bits(ctrl, eiw, CXL_HDM_DECODER0_CTRL_IW_MASK);
> +	*ctrl |= CXL_HDM_DECODER0_CTRL_COMMIT;
> +}
> +
> +static void cxld_set_type(const struct cxl_decoder_config *config, u32 *ctrl)
> +{
> +	u32p_replace_bits(ctrl,
> +			  !!(config->target_type == CXL_DECODER_HOSTONLYMEM),
> +			  CXL_HDM_DECODER0_CTRL_HOSTONLY);
> +}
> +
> +/*
> + * Per CXL 2.0 8.2.5.12.20 Committing Decoder Programming, hardware must set
> + * committed or error within 10ms, but just be generous with 20ms to account for
> + * clock skew and other marginal behavior
> + */
> +#define COMMIT_TIMEOUT_MS 20
> +int cxld_await_commit(void __iomem *hdm, int id)
> +{
> +	u32 ctrl;
> +	int i;
> +
> +	for (i = 0; i < COMMIT_TIMEOUT_MS; i++) {
> +		ctrl = readl(hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> +		if (FIELD_GET(CXL_HDM_DECODER0_CTRL_COMMIT_ERROR, ctrl)) {
> +			ctrl &= ~CXL_HDM_DECODER0_CTRL_COMMIT;
> +			writel(ctrl, hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> +			return -EIO;
> +		}
> +		if (FIELD_GET(CXL_HDM_DECODER0_CTRL_COMMITTED, ctrl))
> +			return 0;
> +		fsleep(1000);
> +	}
> +
> +	return -ETIMEDOUT;
> +}
> +EXPORT_SYMBOL_FOR_MODULES(cxld_await_commit, "cxl_core");
> +
> +static u32 cxl_hdm_write_range(void __iomem *hdm,
> +			       const struct cxl_decoder_config *config)
> +{
> +	u64 size = range_len(&config->hpa_range);
> +	u64 base = config->hpa_range.start;
> +	int id = config->id;
> +	u32 ctrl;
> +
> +	ctrl = readl(hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> +	cxld_set_interleave(config, &ctrl);
> +	cxld_set_type(config, &ctrl);
> +
> +	writel(upper_32_bits(base), hdm + CXL_HDM_DECODER0_BASE_HIGH_OFFSET(id));
> +	writel(lower_32_bits(base), hdm + CXL_HDM_DECODER0_BASE_LOW_OFFSET(id));
> +	writel(upper_32_bits(size), hdm + CXL_HDM_DECODER0_SIZE_HIGH_OFFSET(id));
> +	writel(lower_32_bits(size), hdm + CXL_HDM_DECODER0_SIZE_LOW_OFFSET(id));
> +	return ctrl;
> +}
> +
> +void cxl_commit_start_endpoint(const struct cxl_endpoint_decoder_settings *settings,
> +			       void __iomem *hdm)
> +{
> +	int id = settings->config.id;
> +	u32 ctrl;
> +
> +	ctrl = cxl_hdm_write_range(hdm, &settings->config);
> +	writel(upper_32_bits(settings->skip), hdm + CXL_HDM_DECODER0_SKIP_HIGH(id));
> +	writel(lower_32_bits(settings->skip), hdm + CXL_HDM_DECODER0_SKIP_LOW(id));
> +	writel(ctrl, hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> +}
> +EXPORT_SYMBOL_FOR_MODULES(cxl_commit_start_endpoint, "cxl_core");
> +
> +void cxl_commit_start_switch(const struct cxl_decoder_config *config,
> +			     u64 targets, void __iomem *hdm)
> +{
> +	int id = config->id;
> +	u32 ctrl;
> +
> +	ctrl = cxl_hdm_write_range(hdm, config);
> +	writel(upper_32_bits(targets), hdm + CXL_HDM_DECODER0_TL_HIGH(id));
> +	writel(lower_32_bits(targets), hdm + CXL_HDM_DECODER0_TL_LOW(id));
> +	writel(ctrl, hdm + CXL_HDM_DECODER0_CTRL_OFFSET(id));
> +}
> +EXPORT_SYMBOL_FOR_MODULES(cxl_commit_start_switch, "cxl_core");