linux-kernel - Re: [PATCH] mmc: omap_hsmmc: don't print uninitialized variables

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Message-ID: <56A78838.3050400@ti.com>
Date:	Tue, 26 Jan 2016 16:52:40 +0200
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Arnd Bergmann <arnd@...db.de>, Ulf Hansson <ulf.hansson@...aro.org>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	Andreas Fenkart <afenkart@...il.com>,
	Tony Lindgren <tony@...mide.com>,
	Roger Quadros <rogerq@...com>, <linux-mmc@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: omap_hsmmc: don't print uninitialized variables

On 01/25/2016 05:50 PM, Arnd Bergmann wrote:
> When DT based probing is used but the DMA request fails, the
> driver will print uninitialized stack data from the rx_req
> and tx_req variables, as indicated by this warning:
> 
> drivers/mmc/host/omap_hsmmc.c: In function 'omap_hsmmc_probe':
> drivers/mmc/host/omap_hsmmc.c:2162:3: warning: 'rx_req' may be used uninitialized in this function [-Wmaybe-uninitialized]
>    dev_err(mmc_dev(host->mmc), "unable to obtain RX DMA engine channel %u\n", rx_req);
> 
> This restructures the function to separate the simple DT probe
> from the more complex platform data code path, and only
> prints the information that is actually available and
> needed in case of an error, which makes it nicer to read
> and avoids the warning.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/mmc/host/omap_hsmmc.c | 48 +++++++++++++++++++++----------------------
>  1 file changed, 23 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
> index b6639ea0bf18..e06b1881b6a1 100644
> --- a/drivers/mmc/host/omap_hsmmc.c
> +++ b/drivers/mmc/host/omap_hsmmc.c
> @@ -2002,8 +2002,6 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>  	struct resource *res;
>  	int ret, irq;
>  	const struct of_device_id *match;
> -	dma_cap_mask_t mask;
> -	unsigned tx_req, rx_req;
>  	const struct omap_mmc_of_data *data;
>  	void __iomem *base;
>  
> @@ -2133,7 +2131,17 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>  
>  	omap_hsmmc_conf_bus_power(host);
>  
> -	if (!pdev->dev.of_node) {
> +	host->tx_chan = dma_request_slave_channel(&pdev->dev, "tx");
> +	host->rx_chan = dma_request_slave_channel(&pdev->dev, "rx");
> +	if (!host->tx_chan || !host->rx_chan) {

While it is really unlikely that we are failing to get only one of the
channels... It means anyway that the omap_hsmmc is not usable, but we will
still try to get via legacy mode and there is a chance that we might get some
channel.

Too bad that I can not send the conversion to dma_request_chan() yet due to
missing things in arch...

It might be simpler to just remove the printout of the rx/tx_req from the
dev_err() when reporting failed channel requests...

> +		dma_cap_mask_t mask;
> +		unsigned tx_req, rx_req;
> +
> +		dev_err(mmc_dev(host->mmc), "falling back to manual DMA configuration\n");
> +
> +		dma_cap_zero(mask);
> +		dma_cap_set(DMA_SLAVE, mask);
> +
>  		res = platform_get_resource_byname(pdev, IORESOURCE_DMA, "tx");
>  		if (!res) {
>  			dev_err(mmc_dev(host->mmc), "cannot get DMA TX channel\n");
> @@ -2141,6 +2149,12 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>  			goto err_irq;
>  		}
>  		tx_req = res->start;
> +		host->tx_chan = dma_request_channel(mask, omap_dma_filter_fn, &tx_req);
> +		if (!host->rx_chan) {
> +			dev_err(mmc_dev(host->mmc), "unable to obtain TX DMA engine channel %u\n", tx_req);
> +			ret = -ENXIO;
> +			goto err_irq;
> +		}
>  
>  		res = platform_get_resource_byname(pdev, IORESOURCE_DMA, "rx");
>  		if (!res) {
> @@ -2149,29 +2163,13 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>  			goto err_irq;
>  		}
>  		rx_req = res->start;
> -	}
> -
> -	dma_cap_zero(mask);
> -	dma_cap_set(DMA_SLAVE, mask);
> -
> -	host->rx_chan =
> -		dma_request_slave_channel_compat(mask, omap_dma_filter_fn,
> -						 &rx_req, &pdev->dev, "rx");
> +		host->tx_chan = dma_request_channel(mask, omap_dma_filter_fn, &rx_req);
>  
> -	if (!host->rx_chan) {
> -		dev_err(mmc_dev(host->mmc), "unable to obtain RX DMA engine channel %u\n", rx_req);
> -		ret = -ENXIO;
> -		goto err_irq;
> -	}
> -
> -	host->tx_chan =
> -		dma_request_slave_channel_compat(mask, omap_dma_filter_fn,
> -						 &tx_req, &pdev->dev, "tx");
> -
> -	if (!host->tx_chan) {
> -		dev_err(mmc_dev(host->mmc), "unable to obtain TX DMA engine channel %u\n", tx_req);
> -		ret = -ENXIO;
> -		goto err_irq;
> +		if (!host->tx_chan) {
> +			dev_err(mmc_dev(host->mmc), "unable to obtain RX DMA engine channel %u\n", rx_req);
> +			ret = -ENXIO;
> +			goto err_irq;
> +		}
>  	}
>  
>  	/* Request IRQ for MMC operations */
> 


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