Subject: Re: [PATCH mlx5-next 3/4] net/mlx5: Use query_special_contexts for mkeys

From: Saeed Mahameed <[email-masked]>
Date: Thu, 5 Jan 2023 16:58:22 -0800

On 04 Jan 10:11, Leon Romanovsky wrote:
>From: Or Har-Toov <[email-masked]>
>
>Using query_sepcial_contexts in order to get the correct value of
>terminate_scatter_list_mkey, as FW will change it in some configurations.
>This is done one time when the device is loading and the value is being
>saved in the device context.
>
>Signed-off-by: Or Har-Toov <[email-masked]>
>Reviewed-by: Michael Guralnik <[email-masked]>
>Signed-off-by: Leon Romanovsky <[email-masked]>
>---
> .../net/ethernet/mellanox/mlx5/core/en_main.c |  2 +-
> .../net/ethernet/mellanox/mlx5/core/main.c    | 27 +++++++++++++++++++
> include/linux/mlx5/driver.h                   |  1 +
> 3 files changed, 29 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>index c76f15505a76..33d7a7095988 100644
>--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>@@ -826,7 +826,7 @@ static int mlx5e_alloc_rq(struct mlx5e_params *params,
> 			if (rq->wqe.info.num_frags < (1 << rq->wqe.info.log_num_frags)) {
> 				wqe->data[f].byte_count = 0;
> 				wqe->data[f].lkey =
>-					MLX5_TERMINATE_SCATTER_LIST_LKEY;
>+					mdev->terminate_scatter_list_mkey;
> 				wqe->data[f].addr = 0;
> 			}
> 		}
>diff --git a/drivers/net/ethernet/mellanox/mlx5/core/main.c b/drivers/net/ethernet/mellanox/mlx5/core/main.c
>index 7f5db13e3550..d39d758744a0 100644
>--- a/drivers/net/ethernet/mellanox/mlx5/core/main.c
>+++ b/drivers/net/ethernet/mellanox/mlx5/core/main.c
>@@ -1221,6 +1221,28 @@ static int mlx5_function_teardown(struct mlx5_core_dev *dev, bool boot)
> 	return 0;
> }
>
>+static int mlx5_get_terminate_scatter_list_mkey(struct mlx5_core_dev *dev)
>+{
>+	u32 out[MLX5_ST_SZ_DW(query_special_contexts_out)] = {};
>+	u32 in[MLX5_ST_SZ_DW(query_special_contexts_in)] = {};
>+	int err;
>+
>+	MLX5_SET(query_special_contexts_in, in, opcode,
>+		 MLX5_CMD_OP_QUERY_SPECIAL_CONTEXTS);
>+	err = mlx5_cmd_exec_inout(dev, query_special_contexts, in, out);
>+	if (err)
>+		return err;
>+
>+	if (MLX5_CAP_GEN(dev, terminate_scatter_list_mkey)) {

Why did you execute the command unconditionally if the output is only read
conditionally? 

early exit before executing the command, older FW might fail and driver will
be unusable .. 

>+		dev->terminate_scatter_list_mkey =
>+			cpu_to_be32(MLX5_GET(query_special_contexts_out, out,
>+					     terminate_scatter_list_mkey));
>+		return 0;
>+	}
>+	dev->terminate_scatter_list_mkey = MLX5_TERMINATE_SCATTER_LIST_LKEY;

Another concern, what happens with old driver that is using the hardcoded
value with newer fw ? will it fail ? will it be accepted ? 

The commit message doesn't explain what's going on here very well,
Let's discuss internally before you submit V2.

>+	return 0;
>+}
>+
> static int mlx5_load(struct mlx5_core_dev *dev)
> {
> 	int err;
>@@ -1235,6 +1257,11 @@ static int mlx5_load(struct mlx5_core_dev *dev)
> 	mlx5_events_start(dev);
> 	mlx5_pagealloc_start(dev);
>
>+	err = mlx5_get_terminate_scatter_list_mkey(dev);
>+	if (err) {
>+		mlx5_core_err(dev, "Failed to query special contexts\n");
print the err;
>+		goto err_irq_table;
>+	}

you are querying FW too soon, no issue here but better if you move it after
mlx5_eq_table_create() to use the command EQ rather than the primitive cmd
interface. 

> 	err = mlx5_irq_table_create(dev);
> 	if (err) {
> 		mlx5_core_err(dev, "Failed to alloc IRQs\n");
>diff --git a/include/linux/mlx5/driver.h b/include/linux/mlx5/driver.h
>index d476255c9a3f..5f2c4038d638 100644
>--- a/include/linux/mlx5/driver.h
>+++ b/include/linux/mlx5/driver.h
>@@ -801,6 +801,7 @@ struct mlx5_core_dev {
> 	struct mlx5_rsc_dump    *rsc_dump;
> 	u32                      vsc_addr;
> 	struct mlx5_hv_vhca	*hv_vhca;
>+	__be32			terminate_scatter_list_mkey;
> };
>
> struct mlx5_db {
>-- 
>2.38.1
>