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

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Message-ID:
 <TY3PR01MB113463722674503F2B15F944786ABA@TY3PR01MB11346.jpnprd01.prod.outlook.com>
Date: Wed, 17 Dec 2025 16:16:39 +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 v5 2/6] dmaengine: sh: rz-dmac: Move all CHCTRL updates
 under spinlock

Hi Claudiu,

> -----Original Message-----
> From: Claudiu <claudiu.beznea@...on.dev>
> Sent: 17 December 2025 13:52
> To: vkoul@...nel.org; Fabrizio Castro <fabrizio.castro.jz@...esas.com>; Biju Das
> <biju.das.jz@...renesas.com>; geert+renesas@...der.be; Prabhakar Mahadev Lad <prabhakar.mahadev-
> lad.rj@...renesas.com>
> Cc: Claudiu.Beznea <claudiu.beznea@...on.dev>; dmaengine@...r.kernel.org; linux-
> kernel@...r.kernel.org; Claudiu Beznea <claudiu.beznea.uj@...renesas.com>; stable@...r.kernel.org
> Subject: [PATCH v5 2/6] dmaengine: sh: rz-dmac: Move all 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 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