[PATCH] [RFC] Xilinx MPMC SDMA subsystem

Grant Likely grant.likely at secretlab.ca
Sat Mar 27 10:53:32 EST 2010

I've not got time to review this patch right now, but Sergey and
Steven, you both posted MPMC drivers on the same day; Steven on the
microblaze list and Sergey on the powerpc list.  Can you two please
coordinate and figure out how to mork toward a single driver that will
meet both your needs?  I don't want to have 2 drivers (3 if you count
the ll_temac driver) in mainline for the same hardware interface.


On Wed, Mar 17, 2010 at 12:18 PM, Sergey Temerkhanov
<temerkhanov at cifronik.ru> wrote:
> This patch adds generic support for Xilinx MPMC SoftDMA channels which are
> used by, e.g., LLTEMAC and other IP cores (including custom cores). So, the
> implemented functions include only SDMA channels enumeration and control
> (finding device by phandle property, channel reset, initialization of RX/TX
> links, enabling/disabling IRQs,  IRQ coalescing control and submission of
> descriptors (struct sdma_desc).
> The users of this subsystem are supposed to get the pointer to the struct
> sdma_device by phandle (using sdma_find_device() function), fill the struct
> sdma_client with pointers to the callback functions which are called on rx/tx
> completion, on error, and when sdma_reset is called by any client and then
> register the client with add_client() (sdma_del_client can be used to
> unregister the struct sdma_client)
> Also, some auxiliary functions are provided to check the status of descriptors
> (busy, done, start of packet, end of packet).
> The user is also responsible for maintenance of linked descriptors queue,
> proper initialization of their fields, and submission of the descriptors list
> to SDMA channel. IRQ acknowledge must be performed by user too (calling
> sdma_[rx|tx]_irq_ack respectively in [rx|tx]_complete callbacks). Also on RX
> side user must check the __be32 user[4] fields of descriptors to get the
> information supplied by SDMA channel.
> This code uses SDMA channels in "Tail pointer fashion", i.e. the call to
> sdma_[rx|tx]_init is performed only once after reset and then only sdma_[rx|
> tx]_submit calls are used to update the pointer to the last descriptor in SDMA
> channel.
> Simple bus driver for MPMC is also added by this patch.
> This code is in production use with our internal LLTEMAC driver implementation
> since 2008 and with a few custom cores drivers since 2009.
> This code currently supports only soft MPMCs, i.e., only SDMA channels with
> memory-mapped registers. In order to support channels with DCR, a few
> modifications are needed.
> Any comments and suggestions are appreciated.
> Regards, Sergey Temerkhanov, Cifronic ZAO
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Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.

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