Re: [PATCH v8 2/8] dmaengine: sh: rz-dmac: Move CHCTRL updates under spinlock

[Frank Li]

On Tue, Jan 20, 2026 at 03:33:24PM +0200, Claudiu wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx
> Reviewed-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
>
> Changes in v8:
> - none
>
> Changes in v7:
> - collected tags
>
> 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 36f5fc80a17a..c0f1e77996bd 100644
> --- a/drivers/dma/sh/rz-dmac.c
> +++ b/drivers/dma/sh/rz-dmac.c
> @@ -304,13 +304,10 @@ 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)
> @@ -574,8 +571,8 @@ 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;
>
> @@ -706,7 +703,9 @@ 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
>