Message-Id: <DBR2363A95M1.L9XBNC003490@fairphone.com>
Date: Fri, 01 Aug 2025 13:31:42 +0200
From: "Luca Weiss" <luca.weiss@...rphone.com>
To: "Arnd Bergmann" <arnd@...nel.org>, "Mark Brown" <broonie@...nel.org>,
 "Wesley Cheng" <quic_wcheng@...cinc.com>
Cc: "Arnd Bergmann" <arnd@...db.de>, "Jaroslav Kysela" <perex@...ex.cz>,
 "Takashi Iwai" <tiwai@...e.com>, "Greg Kroah-Hartman"
 <gregkh@...uxfoundation.org>, "Wesley Cheng" <quic_wcheng@...cinc.com>,
 "Dan Carpenter" <dan.carpenter@...aro.org>, <linux-sound@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] ALSA: qc_audio_offload: try to reduce address space
 confusion

Hi Arnd,

On Tue May 13, 2025 at 2:34 PM CEST, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
>
> uaudio_transfer_buffer_setup() allocates a buffer for the subs->dev
> device, and the returned address for the buffer is a CPU local virtual
> address that may or may not be in the linear mapping, as well as a DMA
> address token that is accessible by the USB device, and this in turn
> may or may not correspond to the physical address.
>
> The use in the driver however assumes that these addresses are the
> linear map and the CPU physical address, respectively. Both are
> nonportable here, but in the end only the virtual address gets
> used by converting it to a physical address that gets mapped into
> a second iommu.
>
> Make this more explicit by pulling the conversion out first
> and warning if it is not part of the linear map, and using the
> actual physical address to map into the iommu in place of the
> dma address that may already be iommu-mapped into the usb host.

This patch is breaking USB audio offloading on Qualcomm devices on 6.16,
as tested on sm6350 and sc7280-based smartphones.

[  420.463176] q6afe-dai 3000000.remoteproc:glink-edge:apr:service@4:dais: AFE Port already open
[  420.472676] ------------[ cut here ]------------
[  420.472691] WARNING: CPU: 2 PID: 175 at sound/usb/qcom/qc_audio_offload.c:1056 handle_uaudio_stream_req+0xea8/0x13f8 [snd_usb_audio_qmi]
[  420.472726] Modules linked in: rfcomm zram zsmalloc zstd_compress algif_hash algif_skcipher bnep nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables nfnetlink ipv6 fuse uhid uinput snd_usb_audio_qmi q6asm_dai q6routing q6afe_dai q6usb q6afe_clocks q6adm q6asm snd_q6dsp_common q6afe q6core apr pdr_interface snd_soc_sm8250 snd_soc_qcom
_common snd_soc_qcom_offload_utils snd_soc_qcom_sdw soundwire_bus soc_usb snd_soc_core snd_compress snd_usb_audio ath10k_snoc ath10k_core snd_hwdep snd_usbmidi_lib ath fastrpc snd_pcm mac80211 hci_uart qrtr_smd snd_timer btqca qcom_pd_mapper snd_rawmidi bluetooth libarc4 qcom_pdr_msg cfg80211 snd soundcore ecdh_generic ecc rfkill qrtr qcom_stats qcom_q6v5_pas ipa qcom_pil_info qcom_q6v5 qcom_common
[  420.473018] CPU: 2 UID: 0 PID: 175 Comm: kworker/u32:9 Tainted: G        W           6.16.0 #1-postmarketos-qcom-sm6350 NONE
[  420.473033] Tainted: [W]=WARN
[  420.473038] Hardware name: Fairphone 4 (DT)
[  420.473045] Workqueue: qmi_msg_handler qmi_data_ready_work
[  420.473065] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[  420.473075] pc : handle_uaudio_stream_req+0xea8/0x13f8 [snd_usb_audio_qmi]
[  420.473091] lr : handle_uaudio_stream_req+0xc84/0x13f8 [snd_usb_audio_qmi]
[  420.473104] sp : ffff800082f939a0
[  420.473110] x29: ffff800082f93b10 x28: ffff0000cfb796b8 x27: 0000000000008000
[  420.473128] x26: ffff0000842afc80 x25: ffffa8e75a23b0e0 x24: 0000000000008000
[  420.473145] x23: ffffa8e75a23bcf0 x22: ffff800082f93bd0 x21: 0000000000000000
[  420.473161] x20: ffff800082f93c98 x19: ffff0000939bb740 x18: ffffa8e77925a4d0
[  420.473178] x17: ffffffffffffffff x16: ffffa8e777ef9728 x15: ffffa8e77925a000
[  420.473194] x14: 0000000000000000 x13: 0000000000000dc0 x12: ffff800080000000
[  420.473211] x11: 0000000000000cc0 x10: 0000000000000001 x9 : ffffa8e77944b880
[  420.473227] x8 : ffffd719b5f4d000 x7 : ffff00009033da18 x6 : 0000000000000000
[  420.473244] x5 : 0000000000000000 x4 : ffff800082f93938 x3 : 0000000000000000
[  420.473260] x2 : 0000000000000000 x1 : ffff0000857790c0 x0 : 0000000000000000
[  420.473277] Call trace:
[  420.473283]  handle_uaudio_stream_req+0xea8/0x13f8 [snd_usb_audio_qmi] (P)
[  420.473300]  qmi_invoke_handler+0xbc/0x108
[  420.473314]  qmi_handle_message+0x90/0x1a8
[  420.473326]  qmi_data_ready_work+0x210/0x390
[  420.473339]  process_one_work+0x150/0x3a0
[  420.473351]  worker_thread+0x288/0x480
[  420.473362]  kthread+0x118/0x1e0
[  420.473375]  ret_from_fork+0x10/0x20
[  420.473390] ---[ end trace 0000000000000000 ]---
[  420.479244] qcom-q6afe aprsvc:service:4:4: cmd = 0x100e5 returned error = 0x1
[  420.479540] qcom-q6afe aprsvc:service:4:4: DSP returned error[1]
[  420.479558] qcom-q6afe aprsvc:service:4:4: AFE enable for port 0x7000 failed -22
[  420.479572] q6afe-dai 3000000.remoteproc:glink-edge:apr:service@4:dais: fail to start AFE port 88
[  420.479583] q6afe-dai 3000000.remoteproc:glink-edge:apr:service@4:dais: ASoC error (-22): at snd_soc_dai_prepare() on USB_RX

Reverting this patch makes it work as expected on 6.16.0.

Let me know if I can be of any help to resolve this.

Regards
Luca

>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  sound/usb/qcom/qc_audio_offload.c | 32 ++++++++++++++++++++-----------
>  1 file changed, 21 insertions(+), 11 deletions(-)
>
> diff --git a/sound/usb/qcom/qc_audio_offload.c b/sound/usb/qcom/qc_audio_offload.c
> index c4dde2fa5a1f..46379387c9a5 100644
> --- a/sound/usb/qcom/qc_audio_offload.c
> +++ b/sound/usb/qcom/qc_audio_offload.c
> @@ -78,9 +78,9 @@ struct intf_info {
>  	size_t data_xfer_ring_size;
>  	unsigned long sync_xfer_ring_va;
>  	size_t sync_xfer_ring_size;
> -	unsigned long xfer_buf_iova;
> +	dma_addr_t xfer_buf_iova;
>  	size_t xfer_buf_size;
> -	phys_addr_t xfer_buf_dma;
> +	dma_addr_t xfer_buf_dma;
>  	u8 *xfer_buf_cpu;
>  
>  	/* USB endpoint information */
> @@ -1018,11 +1018,12 @@ static int uaudio_transfer_buffer_setup(struct snd_usb_substream *subs,
>  					struct mem_info_v01 *mem_info)
>  {
>  	struct sg_table xfer_buf_sgt;
> +	dma_addr_t xfer_buf_dma;
>  	void *xfer_buf;
>  	phys_addr_t xfer_buf_pa;
>  	u32 len = xfer_buf_len;
>  	bool dma_coherent;
> -	unsigned long iova;
> +	dma_addr_t xfer_buf_dma_sysdev;
>  	u32 remainder;
>  	u32 mult;
>  	int ret;
> @@ -1045,29 +1046,38 @@ static int uaudio_transfer_buffer_setup(struct snd_usb_substream *subs,
>  		len = MAX_XFER_BUFF_LEN;
>  	}
>  
> -	xfer_buf = usb_alloc_coherent(subs->dev, len, GFP_KERNEL, &xfer_buf_pa);
> +	/* get buffer mapped into subs->dev */
> +	xfer_buf = usb_alloc_coherent(subs->dev, len, GFP_KERNEL, &xfer_buf_dma);
>  	if (!xfer_buf)
>  		return -ENOMEM;
>  
> +	/* Remapping is not possible if xfer_buf is outside of linear map */
> +	xfer_buf_pa = virt_to_phys(xfer_buf);
> +	if (WARN_ON(!page_is_ram(PFN_DOWN(xfer_buf_pa)))) {
> +		ret = -ENXIO;
> +		goto unmap_sync;
> +	}
>  	dma_get_sgtable(subs->dev->bus->sysdev, &xfer_buf_sgt, xfer_buf,
> -			xfer_buf_pa, len);
> -	iova = uaudio_iommu_map(MEM_XFER_BUF, dma_coherent, xfer_buf_pa, len,
> -			      &xfer_buf_sgt);
> -	if (!iova) {
> +			xfer_buf_dma, len);
> +
> +	/* map the physical buffer into sysdev as well */
> +	xfer_buf_dma_sysdev = uaudio_iommu_map(MEM_XFER_BUF, dma_coherent,
> +					       xfer_buf_pa, len, &xfer_buf_sgt);
> +	if (!xfer_buf_dma_sysdev) {
>  		ret = -ENOMEM;
>  		goto unmap_sync;
>  	}
>  
> -	mem_info->dma = xfer_buf_pa;
> +	mem_info->dma = xfer_buf_dma;
>  	mem_info->size = len;
> -	mem_info->iova = PREPEND_SID_TO_IOVA(iova, uaudio_qdev->data->sid);
> +	mem_info->iova = PREPEND_SID_TO_IOVA(xfer_buf_dma_sysdev, uaudio_qdev->data->sid);
>  	*xfer_buf_cpu = xfer_buf;
>  	sg_free_table(&xfer_buf_sgt);
>  
>  	return 0;
>  
>  unmap_sync:
> -	usb_free_coherent(subs->dev, len, xfer_buf, xfer_buf_pa);
> +	usb_free_coherent(subs->dev, len, xfer_buf, xfer_buf_dma);
>  
>  	return ret;
>  }

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