Messages in this thread | | | Date | Tue, 9 Oct 2012 14:30:35 +0200 | From | Jean Delvare <> | Subject | Re: [PATCH 2/13] drivers/media/tuners/mxl5007t.c: use macros for i2c_msg initialization |
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Hi Julia,
On Sun, 7 Oct 2012 17:38:33 +0200, Julia Lawall wrote: > From: Julia Lawall <Julia.Lawall@lip6.fr> > > Introduce use of I2c_MSG_READ/WRITE/OP, for readability.
Next time you send this patch set, please Cc me on every post so that I don't have to hunt for them on lkml.org.
> In each case, a length expressed as an explicit constant is also > re-expressed as the size of the buffer, when this is possible.
This is conceptually wrong, please don't do that. It is perfectly valid to use a buffer which is larger than the message being written or read. When exchanging multiple messages, it is actually quite common to declare only 2 buffers and reuse them:
char reg; char val[2];
struct i2c_msg msg[2] = { { .addr = addr, .flags = 0, .buf = ®, .len = 1 }, { .addr = addr, .flags = I2C_M_RD, .buf = val, .len = 1 }, };
reg = 0x04; i2c_transfer(i2c_adap, msg, 2); /* Do stuff with val */
reg = 0x06; msg[1].len = 2; i2c_transfer(i2c_adap, msg, 2); /* Do stuff with val */
Your conversion would read 2 bytes from register 0x04 instead of 1 in the example above.
I am not opposed to the idea of i2c_msg initialization helper macros, but please don't mix that with actual code changes which could have bad side effects.
Thanks, -- Jean Delvare
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