linux-kernel - Re: [PATCH] dmaengine: dma-jz4780: Break descriptor chains on JZ4740

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Date:   Sun, 14 Jul 2019 17:32:47 -0400
From:   Paul Cercueil <paul@...pouillou.net>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Paul Burton <paul.burton@...s.com>, od@...c.me,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: dma-jz4780: Break descriptor chains on JZ4740

This patch makes the driver work on JZ4740 but fail on other SoCs.
Please ignore this patch, I'll make a V2.

Thanks,
-Paul



Le dim. 30 juin 2019 à 18:52, Paul Cercueil <paul@...pouillou.net> a 
écrit :
> The current driver works perfectly fine on every generation of the
> JZ47xx SoCs, except on the JZ4740.
> 
> There, when hardware descriptors are chained together (with the LINK
> bit set), the next descriptor isn't automatically fetched as it 
> should -
> instead, an interrupt is raised, even if the TIE bit (Transfer 
> Interrupt
> Enable) bit is cleared. When it happens, the DMA transfer seems to be
> stopped (it doesn't chain), and it's uncertain how many bytes have
> actually been transferred.
> 
> Until somebody smarter than me can figure out how to make chained
> descriptors work on the JZ4740, we now disable chained descriptors on
> that particular SoC.
> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  drivers/dma/dma-jz4780.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
> index 263bee76ef0d..aae83389cc10 100644
> --- a/drivers/dma/dma-jz4780.c
> +++ b/drivers/dma/dma-jz4780.c
> @@ -92,6 +92,7 @@
>  #define JZ_SOC_DATA_PROGRAMMABLE_DMA	BIT(1)
>  #define JZ_SOC_DATA_PER_CHAN_PM		BIT(2)
>  #define JZ_SOC_DATA_NO_DCKES_DCKEC	BIT(3)
> +#define JZ_SOC_DATA_BREAK_LINKS		BIT(4)
> 
>  /**
>   * struct jz4780_dma_hwdesc - descriptor structure read by the DMA 
> controller.
> @@ -356,6 +357,7 @@ static struct dma_async_tx_descriptor 
> *jz4780_dma_prep_slave_sg(
>  	void *context)
>  {
>  	struct jz4780_dma_chan *jzchan = to_jz4780_dma_chan(chan);
> +	struct jz4780_dma_dev *jzdma = jz4780_dma_chan_parent(jzchan);
>  	struct jz4780_dma_desc *desc;
>  	unsigned int i;
>  	int err;
> @@ -376,7 +378,8 @@ static struct dma_async_tx_descriptor 
> *jz4780_dma_prep_slave_sg(
> 
>  		desc->desc[i].dcm |= JZ_DMA_DCM_TIE;
> 
> -		if (i != (sg_len - 1)) {
> +		if (i != (sg_len - 1) &&
> +		    !(jzdma->soc_data->flags & JZ_SOC_DATA_BREAK_LINKS)) {
>  			/* Automatically proceeed to the next descriptor. */
>  			desc->desc[i].dcm |= JZ_DMA_DCM_LINK;
> 
> @@ -665,6 +668,7 @@ static enum dma_status 
> jz4780_dma_tx_status(struct dma_chan *chan,
>  static bool jz4780_dma_chan_irq(struct jz4780_dma_dev *jzdma,
>  				struct jz4780_dma_chan *jzchan)
>  {
> +	struct jz4780_dma_desc *desc = jzchan->desc;
>  	uint32_t dcs;
>  	bool ack = true;
> 
> @@ -692,8 +696,10 @@ static bool jz4780_dma_chan_irq(struct 
> jz4780_dma_dev *jzdma,
> 
>  				jz4780_dma_begin(jzchan);
>  			} else if (dcs & JZ_DMA_DCS_TT) {
> -				vchan_cookie_complete(&jzchan->desc->vdesc);
> -				jzchan->desc = NULL;
> +				if (jzchan->curr_hwdesc + 1 == desc->count) {
> +					vchan_cookie_complete(&desc->vdesc);
> +					jzchan->desc = NULL;
> +				}
> 
>  				jz4780_dma_begin(jzchan);
>  			} else {
> @@ -994,6 +1000,7 @@ static int jz4780_dma_remove(struct 
> platform_device *pdev)
>  static const struct jz4780_dma_soc_data jz4740_dma_soc_data = {
>  	.nb_channels = 6,
>  	.transfer_ord_max = 5,
> +	.flags = JZ_SOC_DATA_BREAK_LINKS,
>  };
> 
>  static const struct jz4780_dma_soc_data jz4725b_dma_soc_data = {
> --
> 2.21.0.593.g511ec345e18
>