linux-kernel - Re: helping with remapping vmem for dma

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Date:   Wed, 15 Jun 2022 14:15:33 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Frank Wunderlich <frank-w@...lic-files.de>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: helping with remapping vmem for dma

On 2022-06-15 13:11, Frank Wunderlich wrote:
> Hi,
> 
> i have upported a wifi-driver (mt6625l for armhf) for some time and fall now (at least 5.18) in the
> "rejecting DMA map of vmalloc memory" error [1].
> 
> maybe anybody here can guide me on how to nail it down and maybe fix it.
> 
> as far as i have debugged it, it uses dma_map_single [2] to get dma memory from a previous
> allocated memory region.
> 
> this function "kalDevPortRead" in [2] is used via macro HAL_PORT_RD [3] (used in HAL_READ_RX_PORT
> and HAL_READ_INTR_STATUS in same hal.h file)
> 
> HAL_READ_INTR_STATUS is always called with an empty int array as buf which i guess is not the problem.
> I think the issue is using the use with an preallocated prSDIOCtrl struct (have not completely traced
> it back where it is allocated).

Put simply, if you want to call dma_map_single() on a buffer, then that 
buffer needs to be allocated with kmalloc() (or technically 
alloc_pages(), but then dma_map_page() would make more sense when 
dealing with entire pages.

Robin.

> calls of HAL_PORT_RD/HAL_READ_RX_PORT are in nic{,_rx}.c (with sdio-struct) ([4] as example)
> 
> maybe there is a simple way to get an address in preallocated memory as replacement for the dma_map_simple call (and the unmap of course).
> 
> regards Frank
> 
> [1] https://elixir.bootlin.com/linux/latest/source/include/linux/dma-mapping.h#L327
> [2] https://github.com/frank-w/BPI-R2-4.14/blob/5.18-main/drivers/misc/mediatek/connectivity/wlan/gen2/os/linux/hif/ahb/ahb.c#L940
> [3] https://github.com/frank-w/BPI-R2-4.14/blob/5.18-main/drivers/misc/mediatek/connectivity/wlan/gen2/include/nic/hal.h#L176
> [4] https://github.com/frank-w/BPI-R2-4.14/blob/5.18-main/drivers/misc/mediatek/connectivity/wlan/gen2/nic/nic_rx.c#L3604