linux-kernel - Re: [PATCH v11 2/2] mtd: rawnand: Add Loongson-1 NAND Controller Driver

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Message-ID: <874j1tykgz.fsf@bootlin.com>
Date: Mon, 20 Jan 2025 09:10:04 +0100
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Keguang Zhang <keguang.zhang@...il.com>
Cc: Keguang Zhang via B4 Relay <devnull+keguang.zhang.gmail.com@...nel.org>,
  Richard Weinberger <richard@....at>,  Vignesh Raghavendra
 <vigneshr@...com>,  Rob Herring <robh@...nel.org>,  Krzysztof Kozlowski
 <krzk+dt@...nel.org>,  Conor Dooley <conor+dt@...nel.org>,
  linux-mtd@...ts.infradead.org,  linux-kernel@...r.kernel.org,
  devicetree@...r.kernel.org,  linux-media@...r.kernel.org
Subject: Re: [PATCH v11 2/2] mtd: rawnand: Add Loongson-1 NAND Controller
 Driver


>> >> Don't you need a dma_addr_t here instead? You shall remap the resource.
>> >>
>> > Sorry, I don't quite understand.
>> > 'dma_base' is already of type dma_addr_t.
>>
>> I didn't identify where the dma_base was remapped, but if that's already
>> done then we're good.
>
> Perhaps I misunderstand the usage of dma_map_resource(). dma_base is
> the physical address and will be written to the DMA controller
> register at last.

IIUC, yes and no. It is the remapped address of the physical address you
want to reach, not the physical address itself. The type is dma_addr_t
and not phys_addr_t and you can get a dma address out of a physical
address with a call to dma_map_resource(). The numerical value might be
the same if there is no IO-MMU involved, but the good practice is to
remap anyway.

Thanks,
Miquèl