From: "Valdis Klētnieks" <valdis.kletnieks@vt.edu>
To: "Chan Kim" <ckim@etri.re.kr>
Cc: kernelnewbies@kernelnewbies.org
Subject: Re: returned dma address value of dma_alloc_coherent, is it always in the lower 4GB range?
Date: Tue, 14 Mar 2023 01:14:50 -0400 [thread overview]
Message-ID: <687742.1678770890@turing-police> (raw)
In-Reply-To: <034901d955a7$50a377d0$f1ea6770$@etri.re.kr>
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On Mon, 13 Mar 2023 21:28:28 +0900, "Chan Kim" said:
> which is 32-bit addressable. Even if the device indicates (via the DMA
> mask)
> that it may address the upper 32-bits, consistent allocation will only
> return > 32-bit addresses for DMA if the consistent DMA mask has been
> explicitly changed via dma_set_coherent_mask(). This is true of the
> dma_pool interface as well.
> ------------------------------
> By context I guess it returns the address in lower 32bit address range even
> it the coherent_dma_mask is set to some bigger value.
No, you have that backwards. It's not "even if". It wil give you a 32-bit
address *UNLESS* the driver has called dma_set_coherent_mask() to set a wider
mask *and* the device indicates it supports more than 32 bit addresses...
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next prev parent reply other threads:[~2023-03-14 5:17 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-13 12:28 returned dma address value of dma_alloc_coherent, is it always in the lower 4GB range? Chan Kim
2023-03-14 5:14 ` Valdis Klētnieks [this message]
2023-03-14 8:03 ` Chan Kim
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