linux-kernel - Re: [PATCH v2 1/5] dmaengine: dw-edma: Fix the ch

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Date:   Tue, 3 Oct 2023 14:23:31 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Cai Huoqing <cai.huoqing@...ux.dev>
Cc:     Köry Maincent <kory.maincent@...tlin.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Vinod Koul <vkoul@...nel.org>,
        Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Herve Codina <herve.codina@...tlin.com>
Subject: Re: [PATCH v2 1/5] dmaengine: dw-edma: Fix the ch_count hdma callback

Hi Cai,

On Mon, Oct 02, 2023 at 03:17:45PM +0200, Köry Maincent wrote:
> From: Kory Maincent <kory.maincent@...tlin.com>
> 
> The current check of ch_en enabled to know the maximum number of available
> hardware channels is wrong as it check the number of ch_en register set
> but all of them are unset at probe. This register is set at the
> dw_hdma_v0_core_start function which is run lately before a DMA transfer.
> 
> The HDMA IP have no way to know the number of hardware channels available
> like the eDMA IP, then let set it to maximum channels and let the platform
> set the right number of channels.
> 
> Fixes: e74c39573d35 ("dmaengine: dw-edma: Add support for native HDMA")
> Signed-off-by: Kory Maincent <kory.maincent@...tlin.com>
> ---
> 

> See the following thread mail that talk about this issue:
> https://lore.kernel.org/lkml/20230607095832.6d6b1a73@kmaincent-XPS-13-7390/

Cai, do you have anything to add in regards to this change and to the
discussion available in the thread above? If no, I guess the solution
provided in this patch is the best we can currently come up with.

-Serge(y)

> 
> Changes in v2:
> - Add comment
> ---
>  drivers/dma/dw-edma/dw-hdma-v0-core.c | 17 +++++------------
>  1 file changed, 5 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/dma/dw-edma/dw-hdma-v0-core.c b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> index 00b735a0202a..3e78d4fd3955 100644
> --- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
> +++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
> @@ -65,18 +65,11 @@ static void dw_hdma_v0_core_off(struct dw_edma *dw)
>  
>  static u16 dw_hdma_v0_core_ch_count(struct dw_edma *dw, enum dw_edma_dir dir)
>  {
> -	u32 num_ch = 0;
> -	int id;
> -
> -	for (id = 0; id < HDMA_V0_MAX_NR_CH; id++) {
> -		if (GET_CH_32(dw, id, dir, ch_en) & BIT(0))
> -			num_ch++;
> -	}
> -
> -	if (num_ch > HDMA_V0_MAX_NR_CH)
> -		num_ch = HDMA_V0_MAX_NR_CH;
> -
> -	return (u16)num_ch;
> +	/* The HDMA IP have no way to know the number of hardware channels
> +	 * available, we set it to maximum channels and let the platform
> +	 * set the right number of channels.
> +	 */
> +	return HDMA_V0_MAX_NR_CH;
>  }
>  
>  static enum dma_status dw_hdma_v0_core_ch_status(struct dw_edma_chan *chan)
> -- 
> 2.25.1
>