Re: Report in downstream Debian: mpt3sas broken with xen dom0 with update to 5.10.149 in 5.10.y.

[Christoph Hellwig <hch@infradead.org>]

On Mon, Oct 24, 2022 at 05:26:44PM +0530, Sreekanth Reddy wrote:
> This issue is getting observed after having the below patch changes,
> 2b9aba0c5d58e141e32bb1bb4c7cd91d19f075b8 scsi: mpt3sas: Fix return
> value check of dma_get_required_mask()

Looking at this commit it seems odd.  dma_get_required_mask() should
only be used as an optimization for hardware that actually benefits
from a lower DMA Mask.  That means either classic PCI that requires
DAC cycles, or firmware architectures like aic7xxx that do need
additional overhead.  I don't think either is the case for mpt3sas,
so I think (in addition to fixing up the Xen required mask), mpt3sas
should do something like:

diff --git a/drivers/scsi/mpt3sas/mpt3sas_base.c b/drivers/scsi/mpt3sas/mpt3sas_base.c
index 4e981ccaac4163..295942a8989780 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_base.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_base.c
@@ -2992,8 +2992,7 @@ _base_config_dma_addressing(struct MPT3SAS_ADAPTER *ioc, struct pci_dev *pdev)
 	struct sysinfo s;
 	u64 coherent_dma_mask, dma_mask;
 
-	if (ioc->is_mcpu_endpoint || sizeof(dma_addr_t) == 4 ||
-	    dma_get_required_mask(&pdev->dev) <= DMA_BIT_MASK(32)) {
+	if (ioc->is_mcpu_endpoint) {
 		ioc->dma_mask = 32;
 		coherent_dma_mask = dma_mask = DMA_BIT_MASK(32);
 	/* Set 63 bit DMA mask for all SAS3 and SAS35 controllers */