Re: [PATCH v3 04/18] cxl/pci: Add comments to cxl_hdm_decode_init()

Jonathan Cameron
2025-02-14T15:51:24Z

On Tue, 11 Feb 2025 10:53:34 +0100
Robert Richter <rrichter@amd.com> wrote:

> There are various configuration cases of HDM decoder registers causing
> different code paths. Add comments to cxl_hdm_decode_init() to better
> explain them.
>
> Signed-off-by: Robert Richter <rrichter@amd.com>
> Reviewed-by: Gregory Price <gourry@gourry.net>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Tested-by: Gregory Price <gourry@gourry.net>
> ---
> drivers/cxl/core/pci.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index c49efc419285..6333a01e4f19 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -416,9 +416,17 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
> if (global_ctrl & CXL_HDM_DECODER_ENABLE || (!hdm && info->mem_enabled))
> return devm_cxl_enable_mem(&port->dev, cxlds);
>
> + /*
> + * If the HDM Decoder Capability does not exist and DVSEC was
> + * not setup, the DVSEC based emulation cannot be used.
> + */
> if (!hdm)
> return -ENODEV;
>
> + /*
> + * The HDM Decoder Capability exists but is globally disabled.
> + */
> +
> /*
> * Per CXL 2.0 Section 8.1.3.8.3 and 8.1.3.8.4 DVSEC CXL Range 1 Base
> * [High,Low] when HDM operation is enabled the range register values
> @@ -426,7 +434,8 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
> * DVSEC Range 1,2 to HDM Decoder Range 0,1. So, non-zero info->ranges
> * are expected even though Linux does not require or maintain that
> * match. If at least one DVSEC range is enabled and allowed, skip HDM
> - * Decoder Capability Enable.
> + * Decoder Capability Enable. Else, use the HDM Decoder Capability and
> + * enable it.

As per previous. Having an 'else' comment that refers to what happens if the
following if is true, just adds to confusion :(

So if you are going to move the comment it needs a more substantial rewrite
to reflect that we care 'here' about that last bit only.

> */
> if (!info->mem_enabled) {
> rc = devm_cxl_enable_hdm(&port->dev, cxlhdm);