lkml.org 
[lkml]   [2018]   [Nov]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH 3/7] mtd: spi-nor: add restriction for nmaps in smpt parser
On Thu, 8 Nov 2018 13:58:45 +0000
<Tudor.Ambarus@microchip.com> wrote:

> On 11/08/2018 02:54 PM, Boris Brezillon wrote:
> > On Thu, 8 Nov 2018 11:07:11 +0000
> > <Tudor.Ambarus@microchip.com> wrote:
> >
> >> The map selector is limited to a maximum of 8 bits, allowing
> >> for a maximum of 256 possible map configurations. The total
> >> number of map configurations should be addressable by the
> >> total number of bits described by the detection commands.
> >>
> >> For example: if there are five to eight possible sector map
> >> configurations, at least three configuration detection commands
> >> will be needed to extract three bits of configuration selection
> >> information from the device in order to identify which configuration
> >> is currently in use.
> >>
> >> Suggested-by: Boris Brezillon <boris.brezillon@bootlin.com>
> >
> > I don't remember suggesting this :-).
>
> I see this when you discussed with Yogesh:
>
> + for (nmaps = 0; i< smpt_len; nmaps++) {
> + if(!(smpt[i] & SMPT_DESC_TYPE_MAP)) {
> + i += 2;
> + continue;
> + }
> +
> + if(!map_id_is_valid) {
> + if (nmaps) {
> + ret = NULL;
> + break;
> + }
>
> If I understand correctly, you meant that if there are no detection commands,
> and more than a configuration map, then return an error.

Yes, because in this case we have no way to know what config is
currently selected.

>
> This is correct in my opinion. What I did was to generalize this idea. If smtp
> defines more maps than you can select using detection commands, return error.

AFAICT you're no longer checking that map_id is valid (see below).

>
> +
> + ret = smpt+i;
> + } else if (map_id == SMPT_MAP_ID(smpt[i])) {
> + ret = smpt+i;
> + break;
> + }
> +
> /* increment the table index to the next map */
> i += SMPT_MAP_REGION_COUNT(smpt[i]) + 1;
> }
>
> >
> >> Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
> >> ---
> >> drivers/mtd/spi-nor/spi-nor.c | 15 +++++++++++++--
> >> 1 file changed, 13 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> >> index 59dcedb08691..bd1866d714f2 100644
> >> --- a/drivers/mtd/spi-nor/spi-nor.c
> >> +++ b/drivers/mtd/spi-nor/spi-nor.c
> >> @@ -2868,7 +2868,7 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
> >> const u32 *ret = NULL;
> >> u32 addr;
> >> int err;
> >> - u8 i;
> >> + u8 i, ncmds, nmaps;
> >> u8 addr_width, read_opcode, read_dummy;
> >> u8 read_data_mask, data_byte, map_id;
> >>
> >> @@ -2877,6 +2877,7 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
> >> read_opcode = nor->read_opcode;
> >>
> >> map_id = 0;
> >> + ncmds = 0;
> >> /* Determine if there are any optional Detection Command Descriptors */
> >> for (i = 0; i < smpt_len; i += 2) {
> >> if (smpt[i] & SMPT_DESC_TYPE_MAP)
> >> @@ -2896,6 +2897,7 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
> >> * Configuration that is currently in use.
> >> */
> >> map_id = map_id << 1 | !!(data_byte & read_data_mask);
> >> + ncmds++;
> >> }
> >>
> >> /*
> >> @@ -2905,7 +2907,16 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
> >> *
> >> * Find the matching configuration map.
> >> */
> >> - while (i < smpt_len) {
> >> + for (nmaps = 0; i < smpt_len; nmaps++) {
> >> + /*
> >> + * The map selector is limited to a maximum of 8 bits, allowing
> >> + * for a maximum of 256 possible map configurations. The total
> >> + * number of map configurations should be addressable by the
> >> + * total number of bits described by the detection commands.
> >> + */
> >> + if (ncmds && nmaps >= (1 << (ncmds + 1)))
> >> + break;

You're no longer checking that when ncmds == 0 nmaps has to be 1. So,
say the chip exposed no smpt commands and has several maps defined,
map_id will be 0 while it should have be "undefined". My version
would return an error, but yours tries to find map_id 0.

> >> +
> >
> > Maybe I missed something but it sounds like this change is just
> > optimizing the SPMT parsing a bit, and to be honest, I'm not sure this
> > is really needed. Most of the time, smpt_len will be rather small, so
> > trying to bail out earlier is not bringing much perf improvements.
>
> It's rather a smtp validity check. I want to return an error if there are not
> enough detection commands to identify the map id.

You would have failed the same way without this validity check after a
maximum of smpt_len iterations, right?

\
 
 \ /
  Last update: 2018-11-08 15:16    [W:0.087 / U:0.496 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site