Re: [PATCH v3 4.19.y-cip 13/17] spi: spi-mem: Add a new API to support direct mapping

Lad Prabhakar

Hi Pavel,

Thank you for the review.

-----Original Message-----
From: Pavel Machek <pavel@...>
Sent: 05 January 2021 16:58
To: Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...>
Cc: cip-dev@...; Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...>; Pavel Machek
<pavel@...>; Biju Das <biju.das.jz@...>
Subject: Re: [PATCH v3 4.19.y-cip 13/17] spi: spi-mem: Add a new API to support direct mapping


From: Boris Brezillon <boris.brezillon@...>

commit aa167f3fed0c37e0e4c707d4331d827661f46644 upstream.

Most modern SPI controllers can directly map a SPI memory (or a portion
of the SPI memory) in the CPU address space. Most of the time this
brings significant performance improvements as it automates the whole
process of sending SPI memory operations every time a new region is

This new API allows SPI memory drivers to create direct mappings and
then use them to access the memory instead of using spi_mem_exec_op().
This can be refactored to remove if/else nesting.

+ssize_t spi_mem_dirmap_read(struct spi_mem_dirmap_desc *desc,
+ u64 offs, size_t len, void *buf)
+ struct spi_controller *ctlr = desc->mem->spi->controller;
+ ssize_t ret;
+ if (desc-> != SPI_MEM_DATA_IN)
+ return -EINVAL;
+ if (!len)
+ return 0;
+ if (desc->nodirmap) {
+ ret = spi_mem_no_dirmap_read(desc, offs, len, buf);
+ } else if (ctlr->mem_ops && ctlr->mem_ops->dirmap_read) {
+ ret = spi_mem_access_start(desc->mem);
+ if (ret)
+ return ret;
+ ret = ctlr->mem_ops->dirmap_read(desc, offs, len, buf);
+ spi_mem_access_end(desc->mem);
+ } else {
+ ret = -ENOTSUPP;
+ }
+ return ret;
This can be

if (desc->nodirmap)
return spi_mem_no_dirmap_read(desc, offs, len, buf);
if (!(ctlr->mem_ops && ctlr->mem_ops->dirmap_read))
return -ENOTSUPP;

... normal case goes here...

Same refactoring can be done for dirmap_write.

Code works either way and is not too bad, so... up to you :-).
Agreed. Do you want me to do this as part of this patch or separate patch ?


Best regards,
DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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