linux-kernel - RE: [PATCH v6 2/8] dmaengine: sh: rz-dmac: Move CHCTRL updates under spinlock

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Message-ID:
 <TY3PR01MB1134657B08475CABC31BBE9D186B5A@TY3PR01MB11346.jpnprd01.prod.outlook.com>
Date: Tue, 23 Dec 2025 14:24:47 +0000
From: Biju Das <biju.das.jz@...renesas.com>
To: Claudiu.Beznea <claudiu.beznea@...on.dev>, "vkoul@...nel.org"
	<vkoul@...nel.org>, Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
	"geert+renesas@...der.be" <geert+renesas@...der.be>, Prabhakar Mahadev Lad
	<prabhakar.mahadev-lad.rj@...renesas.com>
CC: Claudiu.Beznea <claudiu.beznea@...on.dev>, "dmaengine@...r.kernel.org"
	<dmaengine@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Claudiu Beznea
	<claudiu.beznea.uj@...renesas.com>, "stable@...r.kernel.org"
	<stable@...r.kernel.org>
Subject: RE: [PATCH v6 2/8] dmaengine: sh: rz-dmac: Move CHCTRL updates under
 spinlock

Hi Claudiu,

> -----Original Message-----
> From: Claudiu <claudiu.beznea@...on.dev>
> Sent: 23 December 2025 13:50
> Subject: [PATCH v6 2/8] dmaengine: sh: rz-dmac: Move CHCTRL updates under spinlock
> 
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> 
> Both rz_dmac_disable_hw() and rz_dmac_irq_handle_channel() update the CHCTRL register. To avoid
> concurrency issues when configuring functionalities exposed by this registers, take the virtual
> channel lock.
> All other CHCTRL updates were already protected by the same lock.
> 
> Previously, rz_dmac_disable_hw() disabled and re-enabled local IRQs, before accessing CHCTRL registers
> but this does not ensure race-free access.
> Remove the local IRQ disable/enable code as well.
> 
> Fixes: 5000d37042a6 ("dmaengine: sh: Add DMAC driver for RZ/G2L SoC")
> Cc: stable@...r.kernel.org
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>

Reviewed-by: Biju Das <biju.das.jz@...renesas.com>

Cheers,
Biju

> ---
> 
> Changes in v6:
> - update patch title and description
> - in rz_dmac_irq_handle_channel() lock only around the
>   updates for the error path and continued using the vc lock
>   as this is the error path and the channel will anyway be
>   stopped; this avoids updating the code with another lock
>   as it was suggested in the review process of v5 and the code
>   remain simpler for a fix, w/o any impact on performance
> 
> Changes in v5:
> - none, this patch is new
> 
>  drivers/dma/sh/rz-dmac.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/dma/sh/rz-dmac.c b/drivers/dma/sh/rz-dmac.c index c8e3d9f77b8a..818d1ef6f0bf
> 100644
> --- a/drivers/dma/sh/rz-dmac.c
> +++ b/drivers/dma/sh/rz-dmac.c
> @@ -298,13 +298,10 @@ static void rz_dmac_disable_hw(struct rz_dmac_chan *channel)  {
>  	struct dma_chan *chan = &channel->vc.chan;
>  	struct rz_dmac *dmac = to_rz_dmac(chan->device);
> -	unsigned long flags;
> 
>  	dev_dbg(dmac->dev, "%s channel %d\n", __func__, channel->index);
> 
> -	local_irq_save(flags);
>  	rz_dmac_ch_writel(channel, CHCTRL_DEFAULT, CHCTRL, 1);
> -	local_irq_restore(flags);
>  }
> 
>  static void rz_dmac_set_dmars_register(struct rz_dmac *dmac, int nr, u32 dmars) @@ -569,8 +566,8 @@
> static int rz_dmac_terminate_all(struct dma_chan *chan)
>  	unsigned int i;
>  	LIST_HEAD(head);
> 
> -	rz_dmac_disable_hw(channel);
>  	spin_lock_irqsave(&channel->vc.lock, flags);
> +	rz_dmac_disable_hw(channel);
>  	for (i = 0; i < DMAC_NR_LMDESC; i++)
>  		lmdesc[i].header = 0;
> 
> @@ -707,7 +704,9 @@ static void rz_dmac_irq_handle_channel(struct rz_dmac_chan *channel)
>  	if (chstat & CHSTAT_ER) {
>  		dev_err(dmac->dev, "DMAC err CHSTAT_%d = %08X\n",
>  			channel->index, chstat);
> -		rz_dmac_ch_writel(channel, CHCTRL_DEFAULT, CHCTRL, 1);
> +
> +		scoped_guard(spinlock_irqsave, &channel->vc.lock)
> +			rz_dmac_ch_writel(channel, CHCTRL_DEFAULT, CHCTRL, 1);
>  		goto done;
>  	}
> 
> --
> 2.43.0