From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: John Garry <john.g.garry@oracle.com>,
James.Bottomley@HansenPartnership.com,
martin.petersen@oracle.com, m.szyprowski@samsung.com, hch@lst.de,
linux-scsi@vger.kernel.org, iommu@lists.linux.dev,
ionut.nechita@windriver.com
Subject: Re: [PATCH 1/2] dma-mapping: make dma_max_mapping_size() return 0 for no DMA capability
Date: Thu, 2 Jul 2026 16:11:16 +0200 [thread overview]
Message-ID: <20260702141116.GA22720@lst.de> (raw)
In-Reply-To: <7c9720fd-c615-481c-ba4d-f5e0efbdd7f0@arm.com>
On Mon, Jun 29, 2026 at 12:09:42PM +0100, Robin Murphy wrote:
>> > Additionally, could this cause invalid zero-sized block layer queue
>> limits
>> > in MMC drivers? In drivers/mmc/host/bcm2835.c:bcm2835_add_host(), the
>> > return value clamps max_req_size:
>> >
>> > mmc->max_req_size = min_t(size_t, 524288,
>> dma_max_mapping_size(dev));
>>
>> bcm2835.c is a platform device driver, and platform devices have their
>> dev->dma_mask set in setup_pdev_dma_masks()
>>
>> Indeed, that driver does have a non-DMA mode of operation, but that looks
>> to be selected independent of whether dev->dma_mask is set.
>
> That one seems pretty bogus already, given that DMA mode is apparently
> dependent on an external DMA channel, so "dev" is the wrong device to check
> (should be dmaengine_get_dma_device()), while conversely
> dma_max_mapping_size(anything) is a questionably meaningless number for PIO
> mode... :/
Yeah. It would be good to get this fixed before this change hits mainline,
though.
next prev parent reply other threads:[~2026-07-02 14:11 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-29 8:53 [PATCH 0/2] Drop SCSI core dev->dma_mask check John Garry
2026-06-29 8:53 ` [PATCH 1/2] dma-mapping: make dma_max_mapping_size() return 0 for no DMA capability John Garry
2026-06-29 9:10 ` sashiko-bot
2026-06-29 10:11 ` Robin Murphy
2026-06-29 10:46 ` John Garry
2026-06-29 11:09 ` Robin Murphy
2026-07-02 14:11 ` Christoph Hellwig [this message]
2026-07-02 14:32 ` John Garry
2026-07-02 14:11 ` Christoph Hellwig
2026-06-29 8:53 ` [PATCH 2/2] scsi: core: Drop dev->dma_mask check in evaluating max_sectors John Garry
2026-07-02 14:12 ` Christoph Hellwig
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