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Date: Tue, 24 Nov 2020 22:51:49 +0530
From: Vinod Koul <vkoul@...nel.org>
To: "Reddy, MallikarjunaX" <mallikarjunax.reddy@...ux.intel.com>
Cc: dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
robh+dt@...nel.org, linux-kernel@...r.kernel.org,
andriy.shevchenko@...el.com, chuanhua.lei@...ux.intel.com,
cheol.yong.kim@...el.com, qi-ming.wu@...el.com,
malliamireddy009@...il.com, peter.ujfalusi@...com
Subject: Re: [PATCH v9 2/2] Add Intel LGM SoC DMA support.
On 24-11-20, 00:29, Reddy, MallikarjunaX wrote:
> Hi Vinod,
>
> Thanks for your valuable review comments. Please see my comments inline.
>
> On 11/21/2020 8:17 PM, Vinod Koul wrote:
> > On 20-11-20, 19:30, Reddy, MallikarjunaX wrote:
> > > Hi Vinod,
> > >
> > > Thanks for the review. My comments inline.
> > >
> > > On 11/19/2020 1:38 AM, Vinod Koul wrote:
> > > > On 12-11-20, 13:38, Amireddy Mallikarjuna reddy wrote:
> > > > > Add DMA controller driver for Lightning Mountain (LGM) family of SoCs.
> > > > >
> > > > > The main function of the DMA controller is the transfer of data from/to any
> > > > > peripheral to/from the memory. A memory to memory copy capability can also
> > > > > be configured.
> > > > >
> > > > > This ldma driver is used for configure the device and channnels for data
> > > > > and control paths.
> > > > >
> > > > > Signed-off-by: Amireddy Mallikarjuna reddy <mallikarjunax.reddy@...ux.intel.com>
> > > > > ---
> > > > > v1:
> > > > > - Initial version.
> > > > You have a cover letter, use that to keep track of these changes
> > > ok.
> > > > > +++ b/drivers/dma/lgm/Kconfig
> > > > > @@ -0,0 +1,9 @@
> > > > > +# SPDX-License-Identifier: GPL-2.0-only
> > > > > +config INTEL_LDMA
> > > > > + bool "Lightning Mountain centralized low speed DMA and high speed DMA controllers"
> > > > Do we have any other speeds :D
> > > No other speeds :-)
> > Right, so possibly drop the speed characterization here!
> "Lightning Mountain centralized DMA controller"
> >
> > > > > +++ b/drivers/dma/lgm/lgm-dma.c
> > > > > @@ -0,0 +1,1742 @@
> > > > > +// SPDX-License-Identifier: GPL-2.0
> > > > > +/*
> > > > > + * Lightning Mountain centralized low speed and high speed DMA controller driver
> > > > > + *
> > > > > + * Copyright (c) 2016 ~ 2020 Intel Corporation.
> > > > I think you mean 2016 - 2020, a dash which refers to duration
> > > ok.
> > > > > +struct dw2_desc {
> > > > > + struct {
> > > > > + u32 len :16;
> > > > > + u32 res0 :7;
> > > > > + u32 bofs :2;
> > > > > + u32 res1 :3;
> > > > > + u32 eop :1;
> > > > > + u32 sop :1;
> > > > > + u32 c :1;
> > > > > + u32 own :1;
> > > > > + } __packed field;
> > > > Another one, looks like folks adding dmaengine patches love this
> > > > approach, second one for the day..
> > > >
> > > > Now why do you need the bit fields, why not use register defines and
> > > > helpers in bitfield.h to help configure the fields See FIELD_GET,
> > > > FIELD_PREP etc
> > > Let me check on this...
> > > > > +struct dma_dev_ops {
> > > > > + int (*device_alloc_chan_resources)(struct dma_chan *chan);
> > > > > + void (*device_free_chan_resources)(struct dma_chan *chan);
> > > > > + int (*device_config)(struct dma_chan *chan,
> > > > > + struct dma_slave_config *config);
> > > > > + int (*device_pause)(struct dma_chan *chan);
> > > > > + int (*device_resume)(struct dma_chan *chan);
> > > > > + int (*device_terminate_all)(struct dma_chan *chan);
> > > > > + void (*device_synchronize)(struct dma_chan *chan);
> > > > > + enum dma_status (*device_tx_status)(struct dma_chan *chan,
> > > > > + dma_cookie_t cookie,
> > > > > + struct dma_tx_state *txstate);
> > > > > + struct dma_async_tx_descriptor *(*device_prep_slave_sg)
> > > > > + (struct dma_chan *chan, struct scatterlist *sgl,
> > > > > + unsigned int sg_len, enum dma_transfer_direction direction,
> > > > > + unsigned long flags, void *context);
> > > > > + void (*device_issue_pending)(struct dma_chan *chan);
> > > > > +};
> > > > Heh! why do you have a copy of dmaengine ops here?
> > > Ok, i will remove the ops and update the code accordingly.
> > > > > +static int ldma_chan_desc_cfg(struct ldma_chan *c, dma_addr_t desc_base,
> > > > > + int desc_num)
> > > > > +{
> > > > > + struct ldma_dev *d = to_ldma_dev(c->vchan.chan.device);
> > > > > +
> > > > > + if (!desc_num) {
> > > > > + dev_err(d->dev, "Channel %d must allocate descriptor first\n",
> > > > > + c->nr);
> > > > > + return -EINVAL;
> > > > > + }
> > > > > +
> > > > > + if (desc_num > DMA_MAX_DESC_NUM) {
> > > > > + dev_err(d->dev, "Channel %d descriptor number out of range %d\n",
> > > > > + c->nr, desc_num);
> > > > > + return -EINVAL;
> > > > > + }
> > > > > +
> > > > > + ldma_chan_desc_hw_cfg(c, desc_base, desc_num);
> > > > > +
> > > > > + c->flags |= DMA_HW_DESC;
> > > > > + c->desc_cnt = desc_num;
> > > > > + c->desc_phys = desc_base;
> > > > So you have a custom API which is used to configure this flag, a number
> > > > and an address. The question is why, can you please help explain this?
> > > LDMA used as general purpose dma(ver == DMA_VER22) and also supports DMA
> > > capability for GSWIP in their network packet processing.( ver > DMA_VER22)
> > Whats GSWIP?
> >
> > > Each Ingress(IGP) & Egress(EGP) ports of CQM use a dma channel.
> > CQM?
> GSWIP stands for Gigabit Switch IP, and CQM is Central Queue Manager.
>
> GSWIP & CQM are the clients for the DMA. These are used in networking
> purpose to increase transfer rates for peripheral like the GSWIP LAN switch.
Please do add that when using these terms, folks outside Intel may not
be aware of these terms.
> >
> > > desc needs to be configure for each dma channel and the remapped address of
> > > the IGP & EGP is desc base adress.
> > Why should this address not passed as src_addr/dst_addr?
> src_addr/dst_addr is the data pointer. Data pointer indicates address
> pointer of data buffer.
>
> ldma_chan_desc_cfg() carries the descriptor address.
>
> The descriptor list entry contains the data pointer, which points to the
> data section in the memory.
>
> So we should not use src_addr/dst_addr as desc base address.
Okay sounds reasonable. why is this using in API here?
> > > CQM client is using ldma_chan_desc_cfg() to configure the descriptior.
> > > > > +static void dma_issue_pending(struct dma_chan *chan)
> > > > > +{
> > > > > + struct ldma_chan *c = to_ldma_chan(chan);
> > > > > + struct ldma_dev *d = to_ldma_dev(c->vchan.chan.device);
> > > > > + unsigned long flags;
> > > > > +
> > > > > + if (d->ver == DMA_VER22) {
> > > > why is this specific to this version?
> > > Only dma0 instance (ver == DMA_VER22) is used as a general purpose slave
> > > DMA. we set both control and datapath here.
> > > Other instances (ver > DMA_VER22) we set only control path. data path is
> > > taken care by dma client(GSWIP).
> > > Only thing needs to do is get the channel, set the descriptor and just 'ON'
> > > the channel.
> > >
> > > CQM is highly low level register configurable/programmable take care about
> > > the the packet processing through the register configurations.
> > DMAengine fwk take care of channel management for clients and
> > transaction management, if you not going to do transactions then why
> > bother with dmaengine ?
> dma0 instance (ver == DMA_VER22) uses DMAengine framework for both channel
> management and transaction management.
>
> Other instances (ver > DMA_VER22) uses DMAengine mainly for channel
> management.
> To initiate the transaction client needs to ON the corresponding channel, So
> dmaengine ops are using to 'ON' and 'OFF' the channels.
Is the addresses for transactions all hardcoded? WHo configures the
transaction in (ver > DMA_VER22)
--
~Vinod
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