linux-kernel - Re: [PATCH 1/1] dmaengine: stm32-dma: avoid 64-bit division in stm32_dma_get_max

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Date:   Tue, 9 Nov 2021 11:20:43 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Amelie Delaunay <amelie.delaunay@...s.st.com>
Cc:     Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        dmaengine@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH 1/1] dmaengine: stm32-dma: avoid 64-bit division in
 stm32_dma_get_max_width

On 03-11-21, 16:33, Amelie Delaunay wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> Using the % operator on a 64-bit variable is expensive and can
> cause a link failure:
> 
> arm-linux-gnueabi-ld: drivers/dma/stm32-dma.o: in function `stm32_dma_get_max_width':
> stm32-dma.c:(.text+0x170): undefined reference to `__aeabi_uldivmod'
> arm-linux-gnueabi-ld: drivers/dma/stm32-dma.o: in function `stm32_dma_set_xfer_param':
> stm32-dma.c:(.text+0x1cd4): undefined reference to `__aeabi_uldivmod'
> 
> As we know that we just want to check the alignment in
> stm32_dma_get_max_width(), there is no need for a full division, and
> using a simple mask is a faster replacement.
> 
> Same in stm32_dma_set_xfer_param(), change this to only allow burst
> transfers if the address is a multiple of the length.
> stm32_dma_get_best_burst just after will take buf_len into account to fix
> burst in case of misalignment.

Applied, thanks

-- 
~Vinod