Hi Jean: * Jean Delvare <khali at linux-fr.org> [2005-08-09 23:13:28 +0200]: > I am implementing I2C block reads in the i2c-viapro driver, and am > looking for testers. I was able to test on my own VT8237R chip, it works > OK, now I'd need to know how it works on older VIA south bridges, namely > the VT8235 and the VT82C686B. South bridges before that (VT82C686A, > VT8233A and older) are supposed not to work according to the datasheets, > but a confirmation would be welcome, who knows, it might simply not be > documented. > > My experimental patch follows. I have enabled the I2C block read > function for all VIA south bridges, so that it can be tested on all > chips. I'll restrict that after the test phase, of course. I fired it up on one of the older chipsets... # lspci 00:00.0 Host bridge: VIA Technologies, Inc. VT82C693A/694x [Apollo PRO133x] (rev c4) 00:01.0 PCI bridge: VIA Technologies, Inc. VT82C598/694x [Apollo MVP3/Pro133x AGP] 00:07.0 ISA bridge: VIA Technologies, Inc. VT82C596 ISA [Mobile South] (rev 23) 00:07.1 IDE interface: VIA Technologies, Inc. VT82C586A/B/VT82C686/A/B/VT823x/A/C PIPC Bus Master IDE (rev 10) 00:07.2 USB Controller: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1 Controller (rev 11) 00:07.3 Host bridge: VIA Technologies, Inc. VT82C596 Power Management (rev 30) # lspci -n 00:00.0 Class 0600: 1106:0691 (rev c4) 00:01.0 Class 0604: 1106:8598 00:07.0 Class 0601: 1106:0596 (rev 23) 00:07.1 Class 0101: 1106:0571 (rev 10) 00:07.2 Class 0c03: 1106:3038 (rev 11) 00:07.3 Class 0600: 1106:3050 (rev 30) As you suspected, it didn't work. # i2cdump -y 0 0x50 i Error: Block read failed, return code 0 > On my system, the dump is down from over 2 seconds without the patch to > below 0.2 second with the patch, which proves how efficient I2C block > reads are and explains why I want to implement this function. I also found something interesting, by accident. With a stock FC4 kernel, the i2cdump clocked at 1.02s total. With 2.6.13-rc6, it took 5.11s! The only relevant difference that I can see is that the FC4 kernel uses HZ of 1000 while my 2.6.13-rc6 kernel uses 100. Because the i2c-viapro is a polling driver, it becomes slower as HZ decreases. I.e. the improvement you are seeing with byte vs. block xfers is quite exaggerated because we poll the device relatively infrequently. *All* the xfers are slower than they could be w/ a non-polling driver. Regards, -- Mark M. Hoffman mhoffman at lightlink.com
