linux-kernel - Re: scatterlist: sg_set_buf() argument must be in linear mapping (sha1: ac4e97abce9b80c020e7113325f49e58b7b15e3f)

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Date:	Mon, 22 Jul 2013 14:58:28 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Jens Axboe <axboe@...nel.dk>, LKML <linux-kernel@...r.kernel.org>,
	Ohad Ben-Cohen <ohad@...ery.com>
Subject: Re: scatterlist: sg_set_buf() argument must be in linear mapping
 (sha1: ac4e97abce9b80c020e7113325f49e58b7b15e3f)

+ Ohad

On 07/22/2013 03:47 AM, Rusty Russell wrote:
> Michal Simek <monstr@...str.eu> writes:
>> Hi Rusty and Jens,
>>
>> I am getting problem with your patch which you have added to the kernel.
>> The problem is with my arm zynq remoteproc driver where
>> I use dma_declare_coherent_memory() to specify memory for remoteproc
>> which is ioremap to the vmalloc area.
>>
>> Based on that buf addr is not inside ram even this coherent memory is in ram.
>> That's why virt_addr_valid(buf) is failing.
> 
> But sg_set_buf() calls virt_to_page(buf).  So does that work?
> 
> I would think calling sg_set_page() directly would be what you want
> here...

Let me take some code from virtio_rpmsg_bus.c to show that problematic part.

bufs_va = dma_alloc_coherent(vdev->dev.parent->parent,
				RPMSG_TOTAL_BUF_SPACE,
				&vrp->bufs_dma, GFP_KERNEL);
vrp->rbufs = bufs_va;
for (i = 0; i < RPMSG_NUM_BUFS / 2; i++) {
	struct scatterlist sg;
	void *cpu_addr = vrp->rbufs + i * RPMSG_BUF_SIZE;

	sg_init_one(&sg, cpu_addr, RPMSG_BUF_SIZE);
}


dma_alloc_coherent returns ioremaped ram address and sg_init_one()
is checking if addr is valid.

It is no problem to call instead of sg_init_one()
	sg_init_table(sg, 1);
	sg_set_page(sg, virt_to_page(cpu_addr), RPMSG_BUF_SIZE, offset_in_page(cpu_addr));


But my question is if SG lists have to be used just for memory which is not remapped.

Ohad: Can you see similar problem with your remoteproc drivers when DEBUG_SG is enabled?

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform



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