linux-kernel - Re: [PATCH v2 2/2] dmaengine: uniphier-mdmac: add UniPhier MIO DMAC driver

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Date:   Wed, 12 Sep 2018 16:31:15 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Vinod <vkoul@...nel.org>
Cc:     "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" 
        <dmaengine@...r.kernel.org>, DTML <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/2] dmaengine: uniphier-mdmac: add UniPhier MIO DMAC driver

2018-09-12 16:26 GMT+09:00 Vinod <vkoul@...nel.org>:
> On 12-09-18, 14:25, Masahiro Yamada wrote:
>> 2018-09-12 13:35 GMT+09:00 Vinod <vkoul@...nel.org>:
>> > On 12-09-18, 12:01, Masahiro Yamada wrote:
>> >> Hi Vinod,
>> >>
>> >>
>> >> 2018-09-11 16:00 GMT+09:00 Vinod <vkoul@...nel.org>:
>> >> > On 24-08-18, 10:41, Masahiro Yamada wrote:
>> >> >
>> >> >> +/* mc->vc.lock must be held by caller */
>> >> >> +static u32 __uniphier_mdmac_get_residue(struct uniphier_mdmac_desc *md)
>> >> >> +{
>> >> >> +     u32 residue = 0;
>> >> >> +     int i;
>> >> >> +
>> >> >> +     for (i = md->sg_cur; i < md->sg_len; i++)
>> >> >> +             residue += sg_dma_len(&md->sgl[i]);
>> >> >
>> >> > so if the descriptor is submitted to hardware, we return the descriptor
>> >> > length, which is not correct.
>> >> >
>> >> > Two cases are required to be handled:
>> >> > 1. Descriptor is in queue (IMO above logic is fine for that, but it can
>> >> > be calculated at descriptor submit and looked up here)
>> >>
>> >> Where do you want it to be calculated?
>> >
>> > where is it calculated now?
>>
>>
>> Please see __uniphier_mdmac_handle().
>>
>>
>> It gets the address and size by sg_dma_address(), sg_dma_len()
>> just before setting them to the hardware registers.
>>
>>
>>        sg = &md->sgl[md->sg_cur];
>>
>>        if (md->dir == DMA_MEM_TO_DEV) {
>>                src_mode = UNIPHIER_MDMAC_CH_MODE__ADDR_INC;
>>                src_addr = sg_dma_address(sg);
>>                dest_mode = UNIPHIER_MDMAC_CH_MODE__ADDR_FIXED;
>>                dest_addr = 0;
>>        } else {
>>                src_mode = UNIPHIER_MDMAC_CH_MODE__ADDR_FIXED;
>>                src_addr = 0;
>>                dest_mode = UNIPHIER_MDMAC_CH_MODE__ADDR_INC;
>>                dest_addr = sg_dma_address(sg);
>>        }
>>
>>
>>
>>
>>
>>
>>
>> >> This hardware provides only simple registers (address and size)
>> >> for one-shot transfer instead of descriptors.
>> >>
>> >> So, I used sgl as-is because I did not see a good reason
>> >> to transform sgl to another data structure.
>> >
>> >
>> >> > this seems missing stuff. Where do you do register calculation for the
>> >> > descriptor and where is slave_config here, how do you know where to
>> >> > send/receive data form/to (peripheral)
>> >>
>> >>
>> >> This dmac is really simple, and un-flexible.
>> >>
>> >> The peripheral address to send/receive data from/to is hard-weird.
>> >> cfg->{src_addr,dst_addr} is not configurable.
>> >>
>> >> Look at __uniphier_mdmac_handle().
>> >> 'dest_addr' and 'src_addr' must be set to 0 for the peripheral.
>> >
>> > Fair enough, what about other values like addr_width and maxburst?
>>
>>
>> None of them is configurable.
>
> what is configurable here :-)

The physical address of the memory, transfer size, direction
are configurable, of course.
But, they are out of scope of device_config hook.


> Who are the users of this DMA?

SD/eMMC controllers.



-- 
Best Regards
Masahiro Yamada