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Date: Fri, 8 Jun 2018 10:43:42 +0200
From: Sascha Hauer <s.hauer@...gutronix.de>
To: Robin Gong <yibin.gong@....com>
Cc: vkoul@...nel.org, dan.j.williams@...el.com,
dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-imx@....com
Subject: Re: [PATCH v2 1/5] dmaengine: imx-sdma: add virt-dma support
On Fri, Jun 08, 2018 at 09:44:46PM +0800, Robin Gong wrote:
> The legacy sdma driver has below limitations or drawbacks:
> 1. Hardcode the max BDs number as "PAGE_SIZE / sizeof(*)", and alloc
> one page size for one channel regardless of only few BDs needed
> most time. But in few cases, the max PAGE_SIZE maybe not enough.
> 2. One SDMA channel can't stop immediatley once channel disabled which
> means SDMA interrupt may come in after this channel terminated.There
> are some patches for this corner case such as commit "2746e2c389f9",
> but not cover non-cyclic.
>
> The common virt-dma overcomes the above limitations. It can alloc bd
> dynamically and free bd once this tx transfer done. No memory wasted or
> maximum limititation here, only depends on how many memory can be requested
> from kernel. For No.2, such issue can be workaround by checking if there
> is available descript("sdmac->desc") now once the unwanted interrupt
> coming. At last the common virt-dma is easier for sdma driver maintain.
>
> The main changes as below:
> --new "sdma_desc" structure containing virt_dma_desc and some members
> which moved from "sdma_channel" such as "num_bd","bd_phys","bd",etc,
> since multi descriptors may exist on virtual dma framework
> rather than only one as before.
> --remove some members of "sdma_channel" structure since it's handled
> by virtual dma common framework, such as "tasklet", "dma_chan",etc.
> --add specific BD0 for channel0 since such bd descriptor is must and
> basic for other dma channel, no need alloc/free as other channel,so
> request it during probe.
> --remove sdma_request_channel(),sdma_tx_submit(),etc.
> --alloc/free bd descriptor added and code changes for virtual dma.
>
> Signed-off-by: Robin Gong <yibin.gong@....com>
> ---
> drivers/dma/Kconfig | 1 +
> drivers/dma/imx-sdma.c | 332 ++++++++++++++++++++++++++++++++-----------------
> 2 files changed, 220 insertions(+), 113 deletions(-)
>
> diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
> index ca1680a..d4a4230 100644
> --- a/drivers/dma/Kconfig
> +++ b/drivers/dma/Kconfig
> @@ -250,6 +250,7 @@ config IMX_SDMA
> tristate "i.MX SDMA support"
> depends on ARCH_MXC
> select DMA_ENGINE
> + select DMA_VIRTUAL_CHANNELS
> help
> Support the i.MX SDMA engine. This engine is integrated into
> Freescale i.MX25/31/35/51/53/6 chips.
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index ccd03c3..8d0c1fd 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -48,6 +48,7 @@
> #include <linux/mfd/syscon/imx6q-iomuxc-gpr.h>
>
> #include "dmaengine.h"
> +#include "virt-dma.h"
>
> /* SDMA registers */
> #define SDMA_H_C0PTR 0x000
> @@ -296,6 +297,31 @@ struct sdma_context_data {
> struct sdma_engine;
>
> /**
> + * struct sdma_desc - descriptor structor for one transfer
> + * @vd descriptor for virt dma
> + * @num_bd max NUM_BD. number of descriptors currently handling
> + * @buf_tail ID of the buffer that was processed
> + * @buf_ptail ID of the previous buffer that was processed
> + * @period_len period length, used in cyclic.
> + * @chn_real_count the real count updated from bd->mode.count
> + * @chn_count the transfer count setuped
> + * @sdmac sdma_channel pointer
> + * @bd pointer of alloced bd
> + */
> +struct sdma_desc {
> + struct virt_dma_desc vd;
> + unsigned int num_bd;
> + dma_addr_t bd_phys;
> + unsigned int buf_tail;
> + unsigned int buf_ptail;
> + unsigned int period_len;
> + unsigned int chn_real_count;
> + unsigned int chn_count;
> + struct sdma_channel *sdmac;
> + struct sdma_buffer_descriptor *bd;
> +};
> +
> +/**
> * struct sdma_channel - housekeeping for a SDMA channel
> *
> * @sdma pointer to the SDMA engine for this channel
> @@ -305,11 +331,10 @@ struct sdma_engine;
> * @event_id0 aka dma request line
> * @event_id1 for channels that use 2 events
> * @word_size peripheral access size
> - * @buf_tail ID of the buffer that was processed
> - * @buf_ptail ID of the previous buffer that was processed
> - * @num_bd max NUM_BD. number of descriptors currently handling
> */
> struct sdma_channel {
> + struct virt_dma_chan vc;
> + struct sdma_desc *desc;
> struct sdma_engine *sdma;
> unsigned int channel;
> enum dma_transfer_direction direction;
> @@ -317,12 +342,6 @@ struct sdma_channel {
> unsigned int event_id0;
> unsigned int event_id1;
> enum dma_slave_buswidth word_size;
> - unsigned int buf_tail;
> - unsigned int buf_ptail;
> - unsigned int num_bd;
> - unsigned int period_len;
> - struct sdma_buffer_descriptor *bd;
> - dma_addr_t bd_phys;
> unsigned int pc_from_device, pc_to_device;
> unsigned int device_to_device;
> unsigned long flags;
> @@ -330,13 +349,10 @@ struct sdma_channel {
> unsigned long event_mask[2];
> unsigned long watermark_level;
> u32 shp_addr, per_addr;
> - struct dma_chan chan;
> spinlock_t lock;
> - struct dma_async_tx_descriptor desc;
> enum dma_status status;
> unsigned int chn_count;
> unsigned int chn_real_count;
These are no longer used here and should be removed.
Sascha
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