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

From: Leon Romanovsky <[email-masked]>
Date: Sun, 8 Jan 2023 12:32:53 +0200

On Thu, Jan 05, 2023 at 04:58:22PM -0800, Saeed Mahameed wrote:
> 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 ..

According to the documentation, this functionality was forever, but you
are presenting valid concern.

> 
> > +		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 ?

It will be accepted and everything will work without glitches.
FW keeps backward compatibility and use MLX5_TERMINATE_SCATTER_LIST_LKEY
internally as a default.

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

NP.

> 
> > +	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.

I'll take a look.

Thanks

> 
> > 	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
> >