RE: [PATCH v5 2/6] dmaengine: sh: rz-dmac: Move all CHCTRL updates under spinlock

[Biju Das]

Hi Claudiu,

> -----Original Message-----
> From: Claudiu <claudiu.beznea@xxxxxxxxx>
> Sent: 17 December 2025 13:52
> To: vkoul@xxxxxxxxxx; Fabrizio Castro <fabrizio.castro.jz@xxxxxxxxxxx>; Biju Das
> <biju.das.jz@xxxxxxxxxxxxxx>; geert+renesas@xxxxxxxxx; Prabhakar Mahadev Lad <prabhakar.mahadev-
> lad.rj@xxxxxxxxxxxxxx>
> Cc: Claudiu.Beznea <claudiu.beznea@xxxxxxxxx>; dmaengine@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>; stable@xxxxxxxxxxxxxxx
> Subject: [PATCH v5 2/6] dmaengine: sh: rz-dmac: Move all CHCTRL updates under spinlock
> 
> From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> 
> Both rz_dmac_disable_hw() and rz_dmac_irq_handle_channel() update the CHCTRL registers. To avoid
> concurrency issues when updating these 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.

Maybe I am missing some thing here about race-access:

	local_irq_save(flags);
  	rz_dmac_ch_writel(channel, CHCTRL_DEFAULT, CHCTRL, 1);

After local_irq_save there won't be any IRQ. So how there
can be a race in IRQ handler.

rz_dmac_irq_handle_channel(){

	rz_dmac_ch_writel(channel, chctrl | CHCTRL_CLREND, CHCTRL, 1);
}


Now adding a vc lock inside interrupt handler the IRQ routine is serialized

Cheers,
Biju