From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
Subject: Re: [PATCH v1 00/16] .map_sg() error cleanup
Date: Thu, 15 Jul 2021 17:53:09 +0100
Message-ID: <20210715165309.GO22278@shell.armlinux.org.uk>
References: <20210715164544.6827-1-logang@deltatee.com>
Mime-Version: 1.0
Return-path: <linux-parisc-owner@vger.kernel.org>
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
        d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type:
        MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To:
        Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date:
        Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:
        List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive;
         bh=SHLau5Ake9xcwQGIQtYxnHJNJDrvOEPwwI40kAVcRog=; b=U8UTMSyF6jF6T0gR2j3D29bvs
        eItdcAl8yoYyPm0BOaqxfp0KAqwYLm3tCNGL3UOXkwf2YVG3YLDETqIWI2+TSILpWhKSi+ZfIepQo
        lLen0o6KgjL85hkzakJ1QZk21sjlzGaASbY+nCfE7vBnPME0Mzb+H5RRmAZ+ZNIKuXcRPERLyqXtq
        VdtZCLk1naymemWuZBuS7BxTMY7tagmEv9JEUS6/HzNAPZKSxBYrlmfrzjhaGexuK2It2kZa4r1/A
        CGDiaLgNp8Hmc8kCrs/WvG5KWvG0MHFhzYQbO2P7Gy0lVzLUmA2kl6R0xkg6NYiRgFN4tL0/sUnPU
Content-Disposition: inline
In-Reply-To: <20210715164544.6827-1-logang@deltatee.com>
Sender: Russell King (Oracle) <linux@armlinux.org.uk>
List-ID: <linux-alpha.vger.kernel.org>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: Logan Gunthorpe <logang@deltatee.com>
Cc: linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, iommu@lists.linux-foundation.org, linux-parisc@vger.kernel.org, xen-devel@lists.xenproject.org, Christoph Hellwig <hch@lst.de>, Marek Szyprowski <m.szyprowski@samsung.com>, Robin Murphy <robin.murphy@arm.com>, Stephen Bates <sbates@raithlin.com>, Martin Oliveira <martin.oliveira@eideticom.com>

On Thu, Jul 15, 2021 at 10:45:28AM -0600, Logan Gunthorpe wrote:
> Hi,
> 
> This series is spun out and expanded from my work to add P2PDMA support
> to DMA map operations[1].
> 
> The P2PDMA work requires distinguishing different error conditions in
> a map_sg operation. dma_map_sgtable() already allows for returning an
> error code (where as dma_map_sg() is only allowed to return zero)
> however, it currently only returns -EINVAL when a .map_sg() call returns
> zero.
> 
> This series cleans up all .map_sg() implementations to return appropriate
> error codes. After the cleanup, dma_map_sg() will still return zero,
> however dma_map_sgtable() will pass the error code from the .map_sg()
> call. Thanks go to Martn Oliveira for doing a lot of the cleanup of the
> obscure implementations.
> 
> The patch set is based off of v5.14-rc1 and a git repo can be found
> here:

Have all the callers for dma_map_sg() been updated to check for error
codes? If not, isn't that a pre-requisit to this patch set?

>From what I see in Linus' current tree, we still have cases today
where the return value of dma_map_sg() is compared with zero to
detect failure, so I think that needs fixing before we start changing
the dma_map_sg() implementation to return negative numbers.

I also notice that there are various places that don't check the
return value - and returning a negative number instead of zero may
well cause random other bits to be set in fields.

So, I think there's a fair amount of work to do in all the drivers
before this change can be considered.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!