From: Yodel Eldar <yodel.eldar@yodel.dev>
To: "Alex Bennée" <alex.bennee@linaro.org>, qemu-devel@nongnu.org
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
"Philippe Mathieu-Daudé" <philmd@linaro.org>,
"Fabiano Rosas" <farosas@suse.de>,
"Laurent Vivier" <lvivier@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"open list:Raspberry Pi" <qemu-arm@nongnu.org>,
"Yodel Eldar" <yodel.eldar@yodel.dev>
Subject: Re: [RFC PATCH] hw/dma: don't allow weird transfer lengths for bcm2835
Date: Fri, 14 Nov 2025 10:05:58 -0600 [thread overview]
Message-ID: <4d6d7e9d-0952-4158-9ef4-6093a16e9dd9@yodel.dev> (raw)
In-Reply-To: <20251111105429.3993300-1-alex.bennee@linaro.org>
On 11/11/2025 04:54, Alex Bennée wrote:
> The datasheet doesn't explicitly say that TXFR_LEN has to be word
> aligned but the fact there is a DMA_D_WIDTH flag to select between 32
> bit and 128 bit strongly implies that is how it works. The downstream
At the bottom of page 38, the datasheet [1] states "the DMA can deal
with byte aligned transfers and will minimise bus traffic by buffering
and packing misaligned accesses."
IIUC, the *_WIDTH info fields are implied as maxima.
[1] https://datasheets.raspberrypi.com/bcm2835/bcm2835-peripherals.pdf
Regards,
Yodel
> rpi kernel also goes to efforts to not write sub-4 byte lengths so
> lets:
next prev parent reply other threads:[~2025-11-14 16:11 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-11 10:54 [RFC PATCH] hw/dma: don't allow weird transfer lengths for bcm2835 Alex Bennée
2025-11-11 11:24 ` Peter Maydell
2025-11-14 16:05 ` Yodel Eldar [this message]
2025-11-14 16:15 ` Peter Maydell
2025-11-14 16:43 ` Alex Bennée
2025-11-14 16:51 ` Florian Kauer
2025-11-16 13:48 ` Yodel Eldar
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