Re: WARNING: drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c:364 vchiq_prepare_bulk_data

From: Stefan Wahren <wahrenst@gmx.net>
To: Arnd Bergmann <arnd@arndb.de>,
	Robin Murphy <robin.murphy@arm.com>,
	Phil Elwell <phil@raspberrypi.com>
Cc: "laurent.pinchart" <laurent.pinchart@ideasonboard.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Christoph Hellwig <hch@lst.de>,
	Florian Fainelli <florian.fainelli@broadcom.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-staging@lists.linux.dev
Subject: Re: WARNING: drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c:364 vchiq_prepare_bulk_data
Date: Tue, 11 Jun 2024 15:09:19 +0200	[thread overview]
Message-ID: <66aafbbd-b90c-4ca6-80a7-233ec0f6dce6@gmx.net> (raw)
In-Reply-To: <87699d92-64f4-4b28-840e-8b320502acb2@app.fastmail.com>

Hi Arnd,

Am 11.06.24 um 14:14 schrieb Arnd Bergmann:
> On Tue, Jun 11, 2024, at 13:37, Stefan Wahren wrote:
>> Am 11.06.24 um 13:08 schrieb Arnd Bergmann:
>>> On Tue, Jun 11, 2024, at 12:47, Stefan Wahren wrote:
>>           if (len == 0)
>>               pr_warn_once("%s: sg_dma_len() == 0\n", __func__);
>>           else if (i && (i != (dma_buffers - 1)) && (len & ~PAGE_MASK))
>>               pr_warn_once("%s: following block not page aligned\n",
>> __func__);
>>           else if (i && (addr & ~PAGE_MASK)) {
>>               pr_warn_once("%s: block %u, DMA address %pad doesn't align
>> with PAGE_MASK 0x%lx\n", __func__, i, &addr, PAGE_MASK);
>>               pr_warn_once("sg_dma_is_swiotlb: %d, dma_flags: %x\n",
>> sg_dma_is_swiotlb(sg), sg->dma_flags);
>>               pr_warn_once("type = %s\n", (type == PAGELIST_WRITE) ?
>> "PAGELIST_WRITE" : "PAGELIST_READ");
>>               if (buf)
>>                   pr_warn_once("buf = %p, count = %zu\n", buf, count);
>>               else
>>                   pr_warn_once("ubuf = %p, count = %zu\n", ubuf, count);
>>           }
>>
>> Output:
>>
>> [   66.184030] create_pagelist: block 1, DMA address 0x00000000f5fc7800
>> doesn't align with PAGE_MASK 0xfffffffffffff000
>> [   66.184056] sg_dma_is_swiotlb: 0, dma_flags: 0
>> [   66.184063] type = PAGELIST_READ
>> [   66.184066] ubuf = 00000000266a70a7, count = 0
sorry my debug attempt for count was pointless. The value is always
decremented to zero at this point. So your suggested change won't have
any effect.
>  From my reading of the code, it's not really meant to handle
> count=0, so maybe the answer for that is to just return an
> error (or possibly success) when there is data attached to
> the request from user space, something like
>
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_dev.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_dev.c
> @@ -328,6 +328,11 @@ static int vchiq_irq_queue_bulk_tx_rx(struct vchiq_instance *instance,
>                  userdata = args->userdata;
>          }
>
> +       if (!args->size) {
> +               ret = 0;
> +               goto out;
> +       }
> +
>          status = vchiq_bulk_transfer(instance, args->handle, NULL, args->data, args->size,
>                                       userdata, args->mode, dir);
>
>
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