linux-kernel - RE: [PATCH 2/2] ntb_hw_switchtec: Check for alignment of the buffer in mw_set

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Date:   Mon, 11 Dec 2017 09:58:29 -0500
From:   "Allen Hubbe" <Allen.Hubbe@...l.com>
To:     "'Logan Gunthorpe'" <logang@...tatee.com>,
        <linux-ntb@...glegroups.com>, <linux-kernel@...r.kernel.org>
Cc:     "'Jon Mason'" <jdmason@...zu.us>
Subject: RE: [PATCH 2/2] ntb_hw_switchtec: Check for alignment of the buffer in mw_set_trans()

From: Logan Gunthorpe
> With Switchtec hardware, the buffer used for a memory window must be
> aligned to its size (the hardware only replaces the lower bits). In
> certain circumstances dma_alloc_coherent() will not provide a buffer
> that adheres to this requirement like when using the CMA and
> CONFIG_CMA_ALIGNMENT is set lower than the buffer size.
> 
> When we get an unaligned buffer mw_set_trans() should return an error.
> We also log an error so we know the cause of the problem.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Cc: Jon Mason <jdmason@...zu.us>
> ---
>  drivers/ntb/hw/mscc/ntb_hw_switchtec.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/ntb/hw/mscc/ntb_hw_switchtec.c b/drivers/ntb/hw/mscc/ntb_hw_switchtec.c
> index 709f37fbe232..984b83bc7dd3 100644
> --- a/drivers/ntb/hw/mscc/ntb_hw_switchtec.c
> +++ b/drivers/ntb/hw/mscc/ntb_hw_switchtec.c
> @@ -315,6 +315,19 @@ static int switchtec_ntb_mw_set_trans(struct ntb_dev *ntb, int pidx, int widx,
>  	if (xlate_pos < 12)
>  		return -EINVAL;
> 
> +	if (addr & ((1 << xlate_pos) - 1)) {

!IS_ALIGNED(addr, BIT_ULL(xlate_pos))

> +		/*
> +		 * In certain circumstances we can get a buffer that is
> +		 * not aligned to its size. (Most of the time
> +		 * dma_alloc_coherent ensures this). This can happen when
> +		 * using large buffers allocated by the CMA
> +		 * (see CMA_CONFIG_ALIGNMENT)
> +		 */
> +		dev_err(&sndev->stdev->dev,
> +			"ERROR: Memory window address is not aligned to it's size!\n");

This would be the only ntb hw driver that prints an error in this situation.  The ntb_mw_get_align() should provide enough information to client drivers to determine the alignment requirements before calling ntb_mw_set_trans().  IMO no need to print here, but let's see what others say.

> +		return -EINVAL;
> +	}
> +
>  	rc = switchtec_ntb_part_op(sndev, ctl, NTB_CTRL_PART_OP_LOCK,
>  				   NTB_CTRL_PART_STATUS_LOCKED);
>  	if (rc)
> --
> 2.11.0