From mboxrd@z Thu Jan 1 00:00:00 1970 From: sricharan@codeaurora.org (Sricharan) Date: Fri, 12 Aug 2016 21:15:32 +0530 Subject: [PATCH 4/8] of: dma: Split of_configure_dma() into mask and ops configuration In-Reply-To: <1651151.fes0RShRSW@avalon> References: <1470696550-3416-1-git-send-email-sricharan@codeaurora.org> <1470696550-3416-5-git-send-email-sricharan@codeaurora.org> <1651151.fes0RShRSW@avalon> Message-ID: <000d01d1f4b0$929cdc30$b7d69490$@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi, >> > The of_configure_dma() function configures both the DMA masks and ops. >> > Moving DMA ops configuration to probe time would thus also delay >> > configuration of the DMA masks, which might not be safe. To avoid issues >> >> Do we know any example cases when it might be unsafe? I think we kind >> of rely on the fact that DMA mapping (and so DMA masks as well) is not >> used before probing the device anyway, because we let the IOMMU >> attachment happen at probe time, which essentially makes any earlier >> attempts to use DMA mapping on such device incorrect. > >I don't know of any such situation, but (if I remember correctly) when I >discussed the IOMMU rework with Arnd Bergman and Will Deacon there was a >concern that someone, somewhere was relying on the mask being set early. > >I personally would like to drop this patch, but it might be difficult to >ensure this wouldn't cause a regression. There should certainly be no DMA >mapping created before IOMMU attachment, but the DMA mask could possibly be >used somewhere else. > Infact i also wanted this to be dropped and to have masks also done along with ops, but thought of getting some feedback if its really needed before probe anywhere. Regards, Sricharan