RE: [PATCH 06/16] ntb: add check and comment for link up to mw_count and mw_get_align

[Allen Hubbe]

From: Logan Gunthorpe
> This patch adds a comment and a check to the ntb_mw_get_align and
> ntb_mw_count functions so that they always fail if the function is
> called before the link is up.
> 
> This is to prevent accidental mis-use in clients that are testing
> on hardware that this doesn't matter for.
> 
> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>

Nak.  This breaks a work around for stability issues on some hardware.  I am ok with changing the comment to say, this is only supported when called after link up.  I would still like to allow these to be called at any time.  Specific hardware drivers like Switchtec may return an error.  Upstream drivers, of course, should call these after link up: patch 5/16 part of this set looks good.

> ---
>  include/linux/ntb.h | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/ntb.h b/include/linux/ntb.h
> index 609e232c00da..de4f800c82b6 100644
> --- a/include/linux/ntb.h
> +++ b/include/linux/ntb.h
> @@ -730,12 +730,16 @@ static inline int ntb_link_disable(struct ntb_dev *ntb)
>   * Hardware and topology may support a different number of memory windows.
>   * Moreover different peer devices can support different number of memory
>   * windows. Simply speaking this method returns the number of possible inbound
> - * memory windows to share with specified peer device.
> + * memory windows to share with specified peer device. Note: this must only be
> + * called when the link is up.
>   *
>   * Return: the number of memory windows.
>   */
>  static inline int ntb_mw_count(struct ntb_dev *ntb, int pidx)
>  {
> +	if (!(ntb_link_is_up(ntb, NULL, NULL) & (1 << pidx)))
> +		return 0;
> +
>  	return ntb->ops->mw_count(ntb, pidx);
>  }
> 
> @@ -751,7 +755,7 @@ static inline int ntb_mw_count(struct ntb_dev *ntb, int pidx)
>   * Get the alignments of an inbound memory window with specified index.
>   * NULL may be given for any output parameter if the value is not needed.
>   * The alignment and size parameters may be used for allocation of proper
> - * shared memory.
> + * shared memory. Note: this must only be called when the link is up.
>   *
>   * Return: Zero on success, otherwise a negative error number.
>   */
> @@ -760,6 +764,9 @@ static inline int ntb_mw_get_align(struct ntb_dev *ntb, int pidx, int widx,
>  				   resource_size_t *size_align,
>  				   resource_size_t *size_max)
>  {
> +	if (!(ntb_link_is_up(ntb, NULL, NULL) & (1 << pidx)))
> +		return -ENOTCONN;
> +
>  	return ntb->ops->mw_get_align(ntb, pidx, widx, addr_align, size_align,
>  				      size_max);
>  }
> --
> 2.11.0