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From: Wolfram Sang <wsa@the-dreams.de>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH RFC 4/4] mmc: host: renesas_sdhi_sys_dmac: Set dma_buswidth value to 32 byte
Date: Thu, 28 Nov 2019 22:07:28 +0100	[thread overview]
Message-ID: <20191128210728.GA864@kunai> (raw)
In-Reply-To: <1574403231-18512-5-git-send-email-yoshihiro.shimoda.uh@renesas.com>

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Hi Shimoda-san,

Interesting series!

> -	.dma_buswidth	= DMA_SLAVE_BUSWIDTH_4_BYTES,
> +	.dma_buswidth	= DMA_SLAVE_BUSWIDTH_32_BYTES,

Two very high level questions:

1) can't we set dma_priv->dma_buswidth at runtime when we know what the
card is capable of? Either DMA_SLAVE_BUSWIDTH_32_BYTES or
DMA_SLAVE_BUSWIDTH_4_BYTES? Then we don't need to fallback to PIO.
AFAIS, we only Gen2 sets .dma_buswidth in of_data, so we could even
remove it from of_data entirely?

2) Just by grepping in mmc/hosts, I see that no driver uses
DMA_SLAVE_BUSWIDTH_32_BYTES. Do you have an idea why? Because it is the
convenient setting which works for all cards?

Thanks and kind regards,

   Wolfram


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  parent reply	other threads:[~2019-11-28 21:07 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-22  6:13 [PATCH RFC 0/4] mmc: host: renesas_sdhi_sys_dmac: change dma_buswidth Yoshihiro Shimoda
2019-11-22  6:13 ` [PATCH RFC 1/4] mmc: host: renesas_sdhi_sys_dmac: Use dma_buswidth instead of hardcoded value Yoshihiro Shimoda
2019-11-26 10:45   ` Ulrich Hecht
2019-11-22  6:13 ` [PATCH RFC 2/4] mmc: host: renesas_sdhi_sys_dmac: Do not fall back to PIO Yoshihiro Shimoda
2019-11-26 10:45   ` Ulrich Hecht
2019-11-22  6:13 ` [PATCH RFC 3/4] mmc: host: renesas_sdhi_sys_dmac: add DMACR setting Yoshihiro Shimoda
2019-11-26 10:46   ` Ulrich Hecht
2019-12-02  8:19     ` Yoshihiro Shimoda
2019-11-22  6:13 ` [PATCH RFC 4/4] mmc: host: renesas_sdhi_sys_dmac: Set dma_buswidth value to 32 byte Yoshihiro Shimoda
2019-11-26 10:46   ` Ulrich Hecht
2019-11-28 21:07   ` Wolfram Sang [this message]
2019-12-02  8:38     ` Yoshihiro Shimoda
2019-12-02  8:54       ` Wolfram Sang
2019-11-26 10:45 ` [PATCH RFC 0/4] mmc: host: renesas_sdhi_sys_dmac: change dma_buswidth Ulrich Hecht
2019-12-02  8:09   ` Yoshihiro Shimoda

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