linux-kernel - RE: [PATCH v2 1/4] dmaengine: xilinx

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Message-ID: <CY1PR02MB16922B2D20C958D8214F7A23DC130@CY1PR02MB1692.namprd02.prod.outlook.com>
Date:   Mon, 8 Jan 2018 17:25:01 +0000
From:   Appana Durga Kedareswara Rao <appanad@...inx.com>
To:     Vinod Koul <vinod.koul@...el.com>
CC:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "lars@...afoo.de" <lars@...afoo.de>,
        "akinobu.mita@...il.com" <akinobu.mita@...il.com>,
        "joabreu@...opsys.com" <joabreu@...opsys.com>,
        "mike.looijmans@...ic.nl" <mike.looijmans@...ic.nl>,
        "kedare06@...il.com" <kedare06@...il.com>,
        "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 1/4] dmaengine: xilinx_dma: populate dma caps properly

Hi,

<Snip>
>> >> +	xdev->common.dst_addr_widths = BIT(addr_width / 8);
>> >> +	xdev->common.src_addr_widths = BIT(addr_width / 8);
>> >
>> >Do you not support trf of 1byte, 2 bytes, or 4 bytes wide transfers?
>> >What is value of addr_width here typically? Usually controllers can
>> >support different widths and this is a surprise that you support only
>> >one value
>>
>> Controller supports address width of 32 and 64.
>
>Then this should have both 32 and 64 values here

Address width is configurable parameter at the h/w level.
Since this IP is a soft IP user can create a design with either 
32-bit or 64-bit address configuration. 
Currently we are reading this configuration through device-tree (xlnx, addr-width property) 
https://git.kernel.org/pub/scm/linux/kernel/git/vkoul/slave-dma.git/tree/Documentation/devicetree/bindings/dma/xilinx/xilinx_dma.txt#n19
Based on the h/w configuration setting the dst_addr_widths/src_addr_widths variables in this patch.
Please let me know if you are still not clear with my explanation will explain in detail... 

Regards,
Kedar.

>
>> addr_width typical values are 32-bit or 64-bit .
>> Here addr_width is device-tree parameter...
>> my understanding of src_addr_widths/dst_addr_widths is, it is a bit
>> mask of the address with in bytes that DMA supports, please correct if my
>understanding is wrong.
>>
>> Regards,
>> Kedar.
>>
>> >
>> >--
>> >~Vinod
>
>--
>~Vinod