linux-kernel - Re: [PATCH v3 6/6] bus: mhi: host: pci_generic: Support independent DMA mask for VFs

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Message-ID: <adba44ewxcgndetgggknfgqzr7ndagmj5fk72w3rgnfn4d7xe6@ulkzzei25qed>
Date: Fri, 5 Sep 2025 20:33:03 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Vivek.Pernamitta@...cinc.com
Cc: mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Vivek Pernamitta <quic_vpernami@...cinc.com>
Subject: Re: [PATCH v3 6/6] bus: mhi: host: pci_generic: Support independent
 DMA mask for VFs

On Thu, Aug 21, 2025 at 06:25:38PM GMT, Vivek.Pernamitta@...cinc.com wrote:
> From: Vivek Pernamitta <quic_vpernami@...cinc.com>
> 
> Certain devices like QDU100 bootloader support only up to a 32-bit DMA
> address range. However, Virtual Functions (VFs) are enabled only after
> the device enters Mission Mode and can support higher DMA address ranges
> (up to 40 bits).
> 
> A 32-bit DMA mask limits addressable space to 4GiB, which is insufficient
> for data transfer requirements over VFs on platforms like QDU100. These
> devices require larger memory regions to be mapped for efficient VF
> operation.
> 
> To address this, configure `dma_mask` independently for Physical Functions
> (PFs) and Virtual Functions (VFs), allowing VFs to use higher DMA mask
> values where supported.
> 
> As per PCIe SR-IOV specification (rev 0.9, Section 1), VFs are capable of
> handling resources associated with the main data movement of the Function.
> 
> This change ensures compatibility with bootloaders that have limited DMA
> capabilities while enabling full VF functionality once the device reaches
> Mission Mode.

Compatibility is with the existing non-SR-IOV devices, isn't it? How does
bootloader comes into picture for them?

- Mani

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