Re: [PATCH v4 01/17] dmaengine: sh: rz-dmac: Move interrupt request after everything is set up

[Claudiu Beznea <claudiu.beznea@tuxon.dev>]

On 4/11/26 15:17, Biju Das wrote:
> 
>> -----Original Message-----
>> From: Claudiu<claudiu.beznea@tuxon.dev>
>> Sent: 11 April 2026 12:43
>> Subject: [PATCH v4 01/17] dmaengine: sh: rz-dmac: Move interrupt request after everything is set up
>>
>> From: Claudiu Beznea<claudiu.beznea.uj@bp.renesas.com>
>>
>> Once the interrupt is requested, the interrupt handler may run immediately.
>> Since the IRQ handler can access channel->ch_base, which is initialized only after requesting the IRQ,
>> this may lead to invalid memory access.
>> Likewise, the IRQ thread may access uninitialized data (the ld_free, ld_queue, and ld_active lists),
>> which may also lead to issues.
>>
>> Request the interrupts only after everything is set up. To keep the error path simpler, use
>> dmam_alloc_coherent() instead of dma_alloc_coherent().
>>
>> Fixes: 5000d37042a6 ("dmaengine: sh: Add DMAC driver for RZ/G2L SoC")
>> Cc:stable@vger.kernel.org
>> Signed-off-by: Claudiu Beznea<claudiu.beznea.uj@bp.renesas.com>
>> ---
>>
>> Changes in v4:
>> - none, this patch is new
>>
>>   drivers/dma/sh/rz-dmac.c | 88 +++++++++++++++-------------------------
>>   1 file changed, 33 insertions(+), 55 deletions(-)
>>
>> diff --git a/drivers/dma/sh/rz-dmac.c b/drivers/dma/sh/rz-dmac.c index 625ff29024de..9f206a33dcc6
>> 100644
>> --- a/drivers/dma/sh/rz-dmac.c
>> +++ b/drivers/dma/sh/rz-dmac.c
>> @@ -981,25 +981,6 @@ static int rz_dmac_chan_probe(struct rz_dmac *dmac,
>>   	channel->index = index;
>>   	channel->mid_rid = -EINVAL;
>>
>> -	/* Request the channel interrupt. */
>> -	scnprintf(pdev_irqname, sizeof(pdev_irqname), "ch%u", index);
>> -	irq = platform_get_irq_byname(pdev, pdev_irqname);
>> -	if (irq < 0)
>> -		return irq;
>> -
>> -	irqname = devm_kasprintf(dmac->dev, GFP_KERNEL, "%s:%u",
>> -				 dev_name(dmac->dev), index);
>> -	if (!irqname)
>> -		return -ENOMEM;
>> -
>> -	ret = devm_request_threaded_irq(dmac->dev, irq, rz_dmac_irq_handler,
>> -					rz_dmac_irq_handler_thread, 0,
>> -					irqname, channel);
>> -	if (ret) {
>> -		dev_err(dmac->dev, "failed to request IRQ %u (%d)\n", irq, ret);
>> -		return ret;
>> -	}
>> -
>>   	/* Set io base address for each channel */
>>   	if (index < 8) {
>>   		channel->ch_base = dmac->base + CHANNEL_0_7_OFFSET + @@ -1012,9 +993,9 @@ static int
>> rz_dmac_chan_probe(struct rz_dmac *dmac,
>>   	}
>>
>>   	/* Allocate descriptors */
>> -	lmdesc = dma_alloc_coherent(&pdev->dev,
>> -				    sizeof(struct rz_lmdesc) * DMAC_NR_LMDESC,
>> -				    &channel->lmdesc.base_dma, GFP_KERNEL);
>> +	lmdesc = dmam_alloc_coherent(&pdev->dev,
>> +				     sizeof(struct rz_lmdesc) * DMAC_NR_LMDESC,
>> +				     &channel->lmdesc.base_dma, GFP_KERNEL);
>>   	if (!lmdesc) {
>>   		dev_err(&pdev->dev, "Can't allocate memory (lmdesc)\n");
>>   		return -ENOMEM;
>> @@ -1030,7 +1011,24 @@ static int rz_dmac_chan_probe(struct rz_dmac *dmac,
>>   	INIT_LIST_HEAD(&channel->ld_free);
>>   	INIT_LIST_HEAD(&channel->ld_active);
>>
>> -	return 0;
>> +	/* Request the channel interrupt. */
>> +	scnprintf(pdev_irqname, sizeof(pdev_irqname), "ch%u", index);
>> +	irq = platform_get_irq_byname(pdev, pdev_irqname);
>> +	if (irq < 0)
>> +		return irq;
>> +
>> +	irqname = devm_kasprintf(dmac->dev, GFP_KERNEL, "%s:%u",
>> +				 dev_name(dmac->dev), index);
>> +	if (!irqname)
>> +		return -ENOMEM;
>> +
>> +	ret = devm_request_threaded_irq(dmac->dev, irq, rz_dmac_irq_handler,
>> +					rz_dmac_irq_handler_thread, 0,
>> +					irqname, channel);
>> +	if (ret)
>> +		dev_err(dmac->dev, "failed to request IRQ %u (%d)\n", irq, ret);
> As per [1], it is redundant.
> 
> [1]
> https://elixir.bootlin.com/linux/v7.0-rc7/source/kernel/irq/devres.c#L108

This is a fix patch, it just moves code around, intended to be backported to 
older kernels (e.g. v6.1, v6.12). However devm_request_result() is introduced in:

commit 55b48e23f5c4
Author: Pan Chuang <panchuang@vivo.com>
Date:   Tue Aug 5 17:29:22 2025 +0800

     genirq/devres: Add error handling in devm_request_*_irq()

     devm_request_threaded_irq() and devm_request_any_context_irq() currently
     don't print any error message when interrupt registration fails.

     This forces each driver to implement redundant error logging - over 2,000
     lines of error messages exist across drivers. Additionally, when
     upper-layer functions propagate these errors without logging, critical
     debugging information is lost.

     Add devm_request_result() helper to unify error reporting via dev_err_probe(),

     Use it in devm_request_threaded_irq() and devm_request_any_context_irq()
     printing device name, IRQ number, handler functions, and error code on failure
     automatically.

     Co-developed-by: Yangtao Li <frank.li@vivo.com>
     Signed-off-by: Yangtao Li <frank.li@vivo.com>
     Signed-off-by: Pan Chuang <panchuang@vivo.com>
     Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
     Link: https://lore.kernel.org/all/20250805092922.135500-2-panchuang@vivo.com

And it is not present in v6.1, v6.12 kernels.

To have a clean backport (at least to the above mentioned kernel versions), 
would be better to have the alignment to devm_request_result() done in a later 
cleanup patch.

Thank you,
Claudiu