linux-kernel - Re: [Patch v5 1/2] dmaengine: add Qualcomm BAM dma driver

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Date:	Fri, 7 Feb 2014 18:42:54 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Andy Gross <agross@...eaurora.org>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-arm-msm@...r.kernel.org
Subject: Re: [Patch v5 1/2] dmaengine: add Qualcomm BAM dma driver

On 02/04, Andy Gross wrote:
> diff --git a/drivers/dma/qcom_bam_dma.c b/drivers/dma/qcom_bam_dma.c
> new file mode 100644
> index 0000000..214250c
> --- /dev/null
> +++ b/drivers/dma/qcom_bam_dma.c
> @@ -0,0 +1,1066 @@
> +/*
> + * QCOM BAM DMA engine driver

Can you please move this down into the comment below?

> + *
> + * Copyright (c) 2013-2014, The Linux Foundation. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 and
> + * only version 2 as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *

And split this out into its own comment block? I think this will
make the lawyers happier.

> + *
> + * QCOM BAM DMA blocks are distributed amongst a number of the on-chip
> + * peripherals on the MSM 8x74.  The configuration of the channels are dependent
> + * on the way they are hard wired to that specific peripheral.  The peripheral
> + * device tree entries specify the configuration of each channel.
> + *
> + * The DMA controller requires the use of external memory for storage of the
> + * hardware descriptors for each channel.  The descriptor FIFO is accessed as a
> + * circular buffer and operations are managed according to the offset within the
> + * FIFO.  After pipe/channel reset, all of the pipe registers and internal state
> + * are back to defaults.
> + *
> + * During DMA operations, we write descriptors to the FIFO, being careful to
> + * handle wrapping and then write the last FIFO offset to that channel's
> + * P_EVNT_REG register to kick off the transaction.  The P_SW_OFSTS register
> + * indicates the current FIFO offset that is being processed, so there is some
> + * indication of where the hardware is currently working.
> + */
[...]
> +
> +/* PIPE CTRL */
> +#define	P_EN			BIT(1)

           ^^^^
Nitpick: Weird tab here?

> +
> +/**
> + * bam_start_dma - start next transaction
> + * @bchan - bam dma channel
> + *
> + * Note: must hold bam dma channel vc.lock

You can use lockdep_assert_held() here to document this
requirement and test for it at runtime.

> + */
> +static void bam_start_dma(struct bam_chan *bchan)

-- 
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