linux-kernel - Re: [PATCH 1/2] mmc: sdhci: Properly set DMA mask

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Message-ID: <20190104174354.GA18110@infradead.org>
Date:   Fri, 4 Jan 2019 09:43:54 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Krishna Reddy <vdumpa@...dia.com>, linux-mmc@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mmc: sdhci: Properly set DMA mask

> +	u64 dma_mask = dma_get_mask(dev);

This is not a driver API.  I think what you want is
dma_get_required_mask to query the mask.  But in that case
you still need to always actually set a mask in the driver as well.

Something like this patch:

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index a22e11a65658..36c61778d8f3 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -3500,6 +3500,13 @@ static int sdhci_set_dma_mask(struct sdhci_host *host)
 	struct device *dev = mmc_dev(mmc);
 	int ret = -EINVAL;
 
+	/*
+	 * Systems that can't address more than 32-bits do not need to use
+	 * 64-bit addressing mode, even if the device supports it.
+	 */
+	if (dma_get_required_mask(dev) <= DMA_BIT_MASK(32))
+		host->flags &= ~SDHCI_USE_64_BIT_DMA;
+
 	if (host->quirks2 & SDHCI_QUIRK2_BROKEN_64_BIT_DMA)
 		host->flags &= ~SDHCI_USE_64_BIT_DMA;