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Wed, 23 Apr 2025 16:56:22 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: dmaengine@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ThreadId: T8f64d9338f7a15a8 Date: Wed, 23 Apr 2025 22:56:01 +0200 From: "Arnd Bergmann" To: "Ben Collins" Cc: dmaengine@vger.kernel.org, "Vinod Koul" , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, "Robin Murphy" Message-Id: <7d914aa8-dc6f-426c-b7fc-dbb03c6b676c@app.fastmail.com> In-Reply-To: <2025042316-nippy-lemur-debd6b@boujee-and-buff> References: <2025042122-bizarre-ibex-b7ed42@boujee-and-buff> <2025042202-uncovered-mongrel-aee116@boujee-and-buff> <2025042204-apricot-tarsier-b7f5a1@boujee-and-buff> <29bdb7e0-6db9-445e-986f-b29af8369c69@app.fastmail.com> <2025042216-hungry-hound-77ecae@boujee-and-buff> <06765168-a36a-4229-b03b-6ea91157237a@app.fastmail.com> <2025042316-nippy-lemur-debd6b@boujee-and-buff> Subject: Re: [PATCH] fsldma: Support 40 bit DMA addresses where capable Content-Type: text/plain Content-Transfer-Encoding: 7bit On Wed, Apr 23, 2025, at 22:41, Ben Collins wrote: > On Wed, Apr 23, 2025 at 03:49:16PM -0500, Arnd Bergmann wrote: >> Looking at the current code I don't see that any more, so it's >> possible that now any DMA is allowed even if there is no >> dma-ranges property at all. > > It's still there. It hardcodes zone_dma_limit to 31-bits: > > arch/powerpc/mm/mem.c: paging_init() > > I'm digging into this more. I'll check back when I have a better > understanding. zone_dma_limit is the other side of this: you need a ZONE_DMA and/or ZONE_DMA32 memory zone that lets a driver allocate buffers from low addresses if the DMA mask is smaller than the available memory. Arnd