linux-kernel - Re: [PATCH v3 09/24] wfx: add hwio.c/hwio.h

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Message-ID: <87lfdp98rw.fsf@codeaurora.org>
Date:   Tue, 22 Dec 2020 17:10:11 +0200
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Jerome Pouiller <Jerome.Pouiller@...abs.com>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S . Miller" <davem@...emloft.net>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-mmc@...r.kernel.org,
        Pali Rohár <pali@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v3 09/24] wfx: add hwio.c/hwio.h

Jerome Pouiller <Jerome.Pouiller@...abs.com> writes:

> +/*
> + * Internal helpers.
> + *
> + * About CONFIG_VMAP_STACK:
> + * When CONFIG_VMAP_STACK is enabled, it is not possible to run DMA on stack
> + * allocated data. Functions below that work with registers (aka functions
> + * ending with "32") automatically reallocate buffers with kmalloc. However,
> + * functions that work with arbitrary length buffers let's caller to handle
> + * memory location. In doubt, enable CONFIG_DEBUG_SG to detect badly located
> + * buffer.
> + */

This sounds very hacky to me, I have understood that you should never
use stack with DMA.

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