linux-kernel - RE: [PATCH v2 2/3] dmaeninge: xilinx_dma: Fix bug in multiple frame stores scenario in vdma

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Date:   Mon, 2 Jan 2017 16:00:51 +0000
From:   Appana Durga Kedareswara Rao <appana.durga.rao@...inx.com>
To:     Jose Abreu <Jose.Abreu@...opsys.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "vinod.koul@...el.com" <vinod.koul@...el.com>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        Soren Brinkmann <sorenb@...inx.com>,
        "moritz.fischer@...us.com" <moritz.fischer@...us.com>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>,
        "luis@...ethencourt.com" <luis@...ethencourt.com>
CC:     "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 2/3] dmaeninge: xilinx_dma: Fix bug in multiple frame
 stores scenario in vdma

Hi Jose Miguel Abreu,

	Thanks for the review...

[snip]...
> 
> I just noticed there is a write to XILINX_DMA_REG_FRMSTORE which, by the
> description in the VDMA databook, allows to modify the total number of
> framebuffers.
> 
> Does it correct this situation: Lets assume VDMA has 10 framebuffers in HW and
> user only submits 5 descriptors. Then vsize will be programmed and VDMA will
> start. The VDMA will start in fb 1, then 2, ... until 5 its all ok. But then after the fb
> 5 the VDMA will jump to fb 6, this fb will have no address because the user only
> submitted 5 addresses so VDMA will try to write to location 0x0 of system mem
> (if using S2MM channel). ?
> 
> If so then there is no race condition, but the HW image that I have does not
> have this register enabled so I was getting this result (memory corruption
> because not all framebuffers had addresses set).

Thanks for the explanation. 
Agree the issue that you mentioned won't come when XILINX_DMA_REG_FRMSTORE
(C_ENABLE_DEBUG_INFO_5 and C_ENABLE_DEBUG_INFO_13) Register is enabled in the IP.
But this register won't get enabled with the default IP configuration (C_ENABLE_DEBUG_INFO_5 and C_ENABLE_DEBUG_INFO_13).

When user is not enabled XILINX_DMA_REG_FRMSTORE in the h/w and submits frames less than h/w capable.
The solution that I am thinking is to throw an error in the driver saying that either enable the
num frame store feature in the IP or submit the frames up to h/w capable what do you think???

Regards,
Kedar.

> 
> Best regards,
> Jose Miguel Abreu
> 
> >
> > Regards,
> > Kedar.
> >
> >> Best regards,
> >> Jose Miguel Abreu
> >>