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

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Message-ID: <20180912072657.GF2766@vkoul-mobl>
Date:   Wed, 12 Sep 2018 12:56:57 +0530
From:   Vinod <vkoul@...nel.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
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

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 :-)

Who are the users of this DMA?

-- 
~Vinod